@article{lee_rouphail_2023, title={Enhanced Crash Frequency Models Using Surrogate Safety Measures from Connected Vehicle Fleet}, ISSN={["2169-4052"]}, DOI={10.1177/03611981231189733}, abstractNote={ As connected vehicle data became available, efforts to employ surrogate safety measures (SSMs) for crash frequency modeling were undertaken. For road safety evaluation, traffic conflicts are quantitatively measured by various SSMs in two dimensions: spatial/temporal proximity (e.g., time-to-collision, TTC) and evasive action (e.g., deceleration rate, DR). However, a single SSM or a single dimension only represents partial images of the true severity of traffic conflicts. Therefore, this study investigates possible enhancements in crash frequency modeling by concurrently using proximity and evasion SSMs. For rear-end crash frequency estimation, five negative binomial regression models and two tree-based models (a regression tree and random forest) were developed. All models were estimated using crashes, traffic volume, and segment length, along with three SSMs (DR, TTC, and modified TTC) extracted from connected vehicle data in Ann Arbor, Michigan. Results show that the multi-SSM model produced a 19.3% reduction in mean absolute error (MAE) compared to the baseline model with no SSM variable, which was significantly higher than those of single-SSM models (4.5−6.9% reductions in MAE). Between all models, the random forest, which is the ensemble machine learning model, produced the highest error reductions (a 44.3% reduction in MAE). These findings show that the concurrent use of proximity and evasion SSMs can yield further enhancements in crash frequency models compared to the singular use of either type of SSM. The proposed modeling method can be used for proactive safety management and assessment using connected vehicle data collected over a short period. }, journal={TRANSPORTATION RESEARCH RECORD}, author={Lee, Taehun and Rouphail, Nagui}, year={2023}, month={Jul} }
 @article{ahmed_karr_rouphail_chase_2023, title={Modeling Framework for Predicting Lane Change Intensity at Freeway Weaving Segments}, volume={4}, ISSN={["2169-4052"]}, url={https://doi.org/10.1177/03611981231165206}, DOI={10.1177/03611981231165206}, abstractNote={ This study proposes a modeling framework for predicting discretionary lane change (DLC) intensity at weaving segments using traffic flow and site data. The database used to develop the models comprises 294 field observations from 19 sites. Two modeling techniques, using regression trees and linear regression, were employed to predict DLCs per hour and DLCs per vehicle. The proposed models were compared with the lane change model for weaving segments in the Highway Capacity Manual (HCM7). The lane change data were clustered by site, which cautioned the applicability of linear regression for this dataset. Nonetheless, both the regression tree and linear regression models yielded high R-squared values, varying from 0.93 to 0.96. The relative root mean squared error (RMSE)—the ratio of the error to the mean values—varied between 0.18 and 0.30. However, a site-specific validation showed that the linear regression models performed poorly for most sites, although measures were taken to cope with outliers, nonlinearity, and interactions. The tree model improved the prediction of DLCs per hour for more than two-thirds of the sites when compared with the mean value at each site. It also performed well in most cases when applied to a site that was omitted from the model development. The HCM7 model performed well when applied to an omitted site. However, it exhibited the highest overall relative RMSE (0.57), underscoring the necessity of advanced modeling tools with additional predictors. We recommend incorporating observations from more extended periods and varying traffic conditions for each site for future research. }, journal={TRANSPORTATION RESEARCH RECORD}, author={Ahmed, Ishtiak and Karr, Alan and Rouphail, Nagui M. and Chase, R. Thomas}, year={2023}, month={Apr} }
 @article{das_ahmed_williams_rouphail_2023, title={Response time of mixed platoons with traditional and autonomous vehicles in field trials: impact assessment on flow stability and safety}, volume={12}, ISSN={["2324-9943"]}, url={https://doi.org/10.1080/23249935.2023.2298498}, DOI={10.1080/23249935.2023.2298498}, abstractNote={This study investigates the response times of autonomous vehicles (AVs) equipped with adaptive cruise control (ACC) and traditional human-driven vehicles (TVs) in mixed traffic scenarios. The primary objective is to assess how these response times impact the stability and safety of mixed traffic flow, considering the growing prevalence of ACC technology in vehicles worldwide. Utilising a trajectory dataset from OpenACC totalling 3389.70 s, this research introduces a response time estimation framework that combines cross-correlation and partial autocorrelation techniques. The study calibrates Gazis, Herman, and Rothery's (GHR) car-following model to evaluate mixed traffic flow stability and employs a modified time-to-collision (MTTC) surrogate for safety analysis. The study also delves into the influence of vehicle manufacturer diversity on study outcomes. Key findings reveal that the AVs exhibit significantly longer response times, ranging from 1.10–3.20 s, compared to the 0.30–1.90-second range of traditional vehicles (p value < 0.005). These extended response times in AVs contribute to prolonged traffic flow instability and increased traffic conflicts. Moreover, the type of lead vehicle does not significantly affect the response times of either AVs or TVs (p value > 0.005). The study also highlights that vehicle manufacturer diversity does not substantially affect these response times. Additionally, the examination of fitted GHR parameters underscores AVs’ heightened sensitivity to spacing and relative speed, providing insights into AV dynamics in the presence of mixed traffic.}, journal={TRANSPORTMETRICA A-TRANSPORT SCIENCE}, author={Das, Tanmay and Ahmed, Ishtiak and Williams, Billy M. and Rouphail, Nagui M.}, year={2023}, month={Dec} }
 @article{das_samandar_autry_rouphail_2023, title={Surrogate Safety Measures: Review and Assessment in Real-World Mixed Traditional and Autonomous Vehicle Platoons}, volume={11}, ISSN={["2169-3536"]}, url={https://doi.org/10.1109/ACCESS.2023.3248628}, DOI={10.1109/ACCESS.2023.3248628}, abstractNote={Surrogate safety measures (SSMs) are critical tools for evaluating the safety performance of mixed traffic. Crashes are rare events, and historical crash data are scarce for mixed traffic that includes autonomous and/ or connected vehicles. Recent safety review papers focus on traditional human-driven vehicles (TVs) and do not encompass advanced technology vehicles such as autonomous vehicles (AVs), connected vehicles (CVs), and connected-autonomous vehicles (CAVs). This study examines the development, implementation, and shortcomings of SSMs and SSM-based models used for mixed traffic safety evaluation. We review the current relevant literature and apply a case study analysis using a real-world mixed traffic dataset. The study summarizes the fundamental SSM guiding concepts, as well as their most significant metrics including threshold values employed in the past for SSMs and SSM-based models. Primary benefits and limitations of examined SSMs and SSM-based models are also underlined. This review reveals significant gaps in the literature that might guide future research paths in SSM-based mixed traffic safety assessment. Critical gaps include the absence of robust SSM threshold selection criteria, the suitability of current SSMs in mixed traffic research, microsimulation modeling that lacks proper calibration and validation, and the absence of a framework for selecting or combining multiple SSMs.}, journal={IEEE ACCESS}, author={Das, Tanmay and Samandar, M. Shoaib and Autry, Meagan Kittle and Rouphail, Nagui M.}, year={2023}, pages={32682–32696} }
 @article{chun_rouphail_samandar_list_yang_akcelik_2022, title={Analytical and Microsimulation Model Calibration and Validation: Application to Roundabouts under Sight-Restricted Conditions}, volume={8}, ISSN={["2169-4052"]}, DOI={10.1177/03611981221115071}, abstractNote={ Analytical models and traffic microsimulation are two widely used platforms for evaluating roundabout operations. The application of the correct inputs and proper specification of calibration parameters should precede the actual simulation, to replicate field traffic conditions. In this sense, simultaneous data collection and estimation of the input, calibration, and validation variables, along with knowledge of their definitions, are crucial. Although simultaneity of data gathering is virtually guaranteed with the use of wide-frame videos captured with an unmanned aerial system (UAS), there are cases where sight distance restrictions may obscure observations of the back of queue and arrival patterns. This paper explores the calibration and validation efforts associated with an analytical platform, SIDRA 9, and a microsimulation model, TransModeler 5, conducted under sight-restricted conditions. Video captured from a drone, followed by trajectory extraction using video processing software, was used to analyze operations on two approaches at a single-lane roundabout. In the process, the team employed a specialized demand estimation method, and developed a novel data collection scheme for estimating the critical headway distribution in TransModeler 5. Because of sight distance constraints, the model validation was limited to the use of the observable system travel time and associated travel speed within the field of view. The comparison results, for both platforms, have confirmed the value of model calibration in more accurately describing field performance. The calibrated models performed differently between the two approaches, with the approach having a larger presence of buses and heavy vehicles yielding slightly poorer results. }, journal={TRANSPORTATION RESEARCH RECORD}, author={Chun, Gyounghoon and Rouphail, Nagui and Samandar, M. Shoaib and List, George and Yang, Guangchuan and Akcelik, Rahmi}, year={2022}, month={Aug} }
 @article{samandar_chun_yang_chase_rouphail_list_2022, title={Capitalizing on Drone Videos to Calibrate Simulation Models for Signalized Intersections and Roundabouts}, volume={6}, ISSN={["2169-4052"]}, DOI={10.1177/03611981221096120}, abstractNote={ Simulation is an indispensable tool for the assessment of highway-related capital investments and operational changes. Model calibration, a challenging task in any simulation study, is a crucial step. The model’s robustness, accuracy, and quality are directly dependent on it. Many parameters exist, and field observations are often lacking to aid in their correct specification. Recently, videos from drones have created a uniquely powerful way to aid this process. Observations of the inputs (demand), outputs (vehicles processed), processing rates (e.g., saturation flow rates), and performance results (times in system, queue dynamics, and delays) are all available simultaneously. For signalized intersections, only the signal timing events are missing, and those data can be obtained from signal timing logs. This paper illustrates how modeling teams can use drone data to calibrate model parameters pertaining to intersection operation. It shows how saturation flow rates can be adjusted for signalized intersections so that queue dynamics and delays can be matched. For roundabouts, it illustrates how critical gaps and move-up times can be adjusted to match field observations of performance. Three real-world settings with associated drone data are used as case study examples. }, journal={TRANSPORTATION RESEARCH RECORD}, author={Samandar, M. Shoaib and Chun, Gyounghoon and Yang, Guangchuan and Chase, Thomas and Rouphail, Nagui M. and List, George F.}, year={2022}, month={Jun} }
 @article{ahmed_karr_rouphail_chase_tanvir_2022, title={Characterizing lane changing behavior and identifying extreme lane changing traits}, volume={4}, ISSN={["1942-7875"]}, url={https://doi.org/10.1080/19427867.2022.2066856}, DOI={10.1080/19427867.2022.2066856}, abstractNote={ABSTRACT This study characterizes lane changing behavior of drivers under differing congestion levels and identifies extreme lane changing traits using high-resolution trajectory data. Total lane change frequency exhibited a reciprocal relationship with congestion level, but the distribution of lane change per vehicle remained unchanged as congestion increased. On average, the speed of trajectories increased by 5.4 ft/s after changing a lane. However, this gain significantly diminished as congestion worsened. Further, the average speed of lane changing vehicles was 3.9 ft/s higher than those that executed no lane changes. Two metrics were employed to identify extreme lane changing behavior: critical time-to-line-crossing (TLCc) and lane changes per unit distance. The lowest 1% TLCc varied between 0.71–1.57 seconds. The highest 1% of lane change rates for all lane changing vehicles was 2.5 lane changes per 1,000 ft traveled. Interestingly, no drivers in thisdataset had both excessive lane changes and lane changes with low TLCc.}, journal={TRANSPORTATION LETTERS-THE INTERNATIONAL JOURNAL OF TRANSPORTATION RESEARCH}, publisher={Informa UK Limited}, author={Ahmed, Ishtiak and Karr, Alan F. and Rouphail, Nagui M. and Chase, R. Thomas and Tanvir, Shams}, year={2022}, month={Apr} }
 @article{das_samandar_rouphail_2022, title={Longitudinal traffic conflict analysis of autonomous and traditional vehicle platoons in field tests via surrogate safety measures}, volume={177}, ISSN={["1879-2057"]}, DOI={10.1016/j.aap.2022.106822}, abstractNote={Autonomous vehicles (AVs) have been introduced into the traffic stream alongside traditional vehicles (TVs) with the expectation of improved transportation safety, efficiency, and reliability. The majority of AV safety research has been done through simulation. The results of such research on the safety performances of AVs are heavily influenced by the methodological framework, algorithms, and assumptions about AV driving characteristics in a simulated environment. There is a need for AV safety research based on real-world settings before any wide-scale deployment of this technology. This paper investigates the impact of the presence of SAE level 2 AVs in the traffic stream in reducing longitudinal traffic conflicts using Surrogate Safety Measures on a real-world open-source database of mixed traffic trajectories. The analysis is conducted for both AV-exclusive and mixed AV-TV platoons. Furthermore, we explore whether the presence of AVs decreases longitudinal traffic conflicts in two-vehicle platoons comprising AV and TV mixed leaders and followers. We find that an exclusive AV platoon behaves similarly to an exclusive TV platoon and produces similar longitudinal conflicts. However, mixed platoons with both AVs and TVs result in a higher number of longitudinal conflicts. Maintaining near-identical leader-follower conditions, we find that the number of conflicts in mixed platoons when an AV follows a TV is higher than when a TV follows an AV. The increase in conflict numbers in a TV-AV mixed platoon can be attributed to AV's longer response time lag. In summary, analyses conducted in this paper indicate that exclusive platoons and pairs of vehicles exhibit fewer longitudinal conflicts than mixed platoons and pairs.}, journal={ACCIDENT ANALYSIS AND PREVENTION}, author={Das, Tanmay and Samandar, M. Shoaib and Rouphail, Nagui}, year={2022}, month={Nov} }
 @article{lee_cunningham_rouphail_2022, title={Movement-based intersection crash frequency modeling}, ISSN={["1943-9970"]}, DOI={10.1080/19439962.2022.2092571}, abstractNote={Abstract Traditional crash frequency models cannot estimate crash frequency for individual traffic movements at an intersection, which precludes the safety evaluation of individual movements and identification of hazardous ones. This paper proposes a movement-based (MB) model that estimates crash frequency for individual movements as well as for the entire intersection. A base model using the safety performance function form in the Highway Safety Manual was also developed for comparison against the MB model. This study used crashes collected for five to eight years at 41 signalized intersections in North Carolina for the model estimation and validation (21 intersections for the estimation and 20 intersections for the validation). The models were validated using cumulative residual plots, test set validation, and in a case study. The test set validation showed that the MB model yielded slight improvements in estimations compared to the base model (1.17%−5.83% reductions in mean absolute error and 3.32%−6.64% reductions in root-mean-square error). The case study showed the MB model correctly identified hazardous traffic movements that had demonstrable safety problems based on observed and estimated crash frequencies. The MB model will enable engineers to identify hazardous movements and approaches to implement safety improvement countermeasures at the deserving locations and movements.}, journal={JOURNAL OF TRANSPORTATION SAFETY & SECURITY}, author={Lee, Taehun and Cunningham, Christopher and Rouphail, Nagui}, year={2022}, month={Jun} }
 @article{amini_xu_rouphail_elefteriadou_aghdashi_2021, title={Capacity Analysis Framework for Freeway Ramp Weaves}, volume={147}, ISSN={["2473-2893"]}, DOI={10.1061/JTEPBS.0000594}, abstractNote={AbstractThe Highway Capacity Manual 6th Edition (HCM6) provides methods for evaluating freeway segments and facilities, including weaving segments. Recent research has cast doubt on the validity of...}, number={12}, journal={JOURNAL OF TRANSPORTATION ENGINEERING PART A-SYSTEMS}, author={Amini, Ehsan and Xu, Dezhong and Rouphail, Nagui M. and Elefteriadou, Lily and Aghdashi, Behzad}, year={2021}, month={Dec} }
 @article{avr_tanvir_rouphail_ahmed_2021, title={Dynamically Collected Local Density using Low-Cost Lidar and its Application to Traffic Models}, volume={5}, ISSN={["2169-4052"]}, DOI={10.1177/03611981211010184}, abstractNote={ This article demonstrates the use of traffic density observations collected dynamically in the vicinity of probe vehicles. Fixed position sensors cannot capture the longitudinal evolution of local traffic density in the corridor. In this research, dynamic traffic density observations were collected in a naturalistic driving setting that was free of any controlled experiment biases. Speed from global positioning system and space headway from a light detection and ranging module was collected on one arterial and one freeway segment, 2 and 4 mi long, respectively. The combined data frequency was approximately 3 Hz. Space headway was used to estimate the local density and consequently to identify the density of a specific location in a corridor. Besides, driver behavior was characterized using the relationship between instantaneous speed and local density under different regimes of the Wiedemann car-following model. Macroscopic traffic stream models were used to investigate the relationship between dynamically collected instantaneous speed and local density. Using the longitudinal evolution of density, precise local density across the corridor can be obtained along with the leader and follower trajectories. A method to identify driver behavior across density ranges was developed for different facility types using a microscopic relationship between instantaneous speed and local density. Overall driving behavior on the freeway segment can be represented by translating the instantaneous speed and local density relationship to macroscopic stream models. }, journal={TRANSPORTATION RESEARCH RECORD}, author={Avr, Azhagan and Tanvir, Shams and Rouphail, Nagui M. and Ahmed, Ishtiak}, year={2021}, month={May} }
 @article{addison_aghdashi_rouphail_2021, title={Evaluating the Effect of Incidents on Freeway Facilities and Updating the Incident Capacity Adjustments for HCM}, volume={2675}, ISSN={["2169-4052"]}, DOI={10.1177/0361198120949530}, abstractNote={ This paper investigates the effect of incidents on freeway segment capacity. Currently, the Highway Capacity Manual (HCM) provides a look-up table linking the remaining segment capacity fraction during an incident to the total and closed number of lanes on the segment. In reality, segment capacity during an incident will tend to vary over time, with the most severe effects felt early on before any type of response is initiated, with congestion progressively improving as the appropriate incident management actions are implemented. By applying a genetic algorithm calibration method on each incident day and calibrating the incident capacity adjustment factors (CAFs), optimal time-dependent CAFs were derived that best represented the effect of incidents on the freeway segment capacity. By analyzing the optimal CAFs, the strongest relationship was revealed to be between the optimal time-dependent CAF and the temporal progression of the incident. A regression model was developed to represent this behavior. This was formulated in a manner that can directly adjust the current HCM’s fixed CAF values (for a specific lane closure configuration) for modeling incidents both in single day, seed file application, or for an entire year reliability analysis. A portion of WB I-540 in Raleigh, NC was selected as the study area in which the proposed method was tested. Between January 2014 and December 2018, the team identified 22 isolated incidents (away from the recurring congestion period) that closed one or two lanes of traffic, creating a distinct congestion pattern. }, number={1}, journal={TRANSPORTATION RESEARCH RECORD}, author={Addison, Jeremy and Aghdashi, Seyedbehzad and Rouphail, Nagui M.}, year={2021}, month={Jan}, pages={224–234} }
 @article{hasnat_bardaka_samandar_rouphail_list_williams_2021, title={Impacts of Private Autonomous and Connected Vehicles on Transportation Network Demand in the Triangle Region, North Carolina}, volume={147}, ISSN={["1943-5444"]}, url={https://doi.org/10.1061/(ASCE)UP.1943-5444.0000649}, DOI={10.1061/(ASCE)UP.1943-5444.0000649}, abstractNote={Abstract Autonomous and connected vehicle technologies have the potential to bring profound changes in travel behavior and transportation network performance with moderate to significant market pen...}, number={1}, journal={JOURNAL OF URBAN PLANNING AND DEVELOPMENT}, publisher={American Society of Civil Engineers (ASCE)}, author={Hasnat, Md. Mehedi and Bardaka, Eleni and Samandar, M. Shoaib and Rouphail, Nagui and List, George and Williams, Billy}, year={2021}, month={Mar} }
 @article{ahmed_warchol_cunningham_rouphail_2021, title={Mobility Assessment of Pedestrian and Bicycle Treatments at Complex Continuous Flow Intersections}, volume={147}, ISSN={["2473-2893"]}, url={https://doi.org/10.1061/JTEPBS.0000512}, DOI={10.1061/JTEPBS.0000512}, abstractNote={AbstractThis study evaluated the mobility performance of pedestrian-bicycle crossing alternatives at continuous flow intersections (CFIs). CFI crossing types were compared with a standard intersect...}, number={5}, journal={JOURNAL OF TRANSPORTATION ENGINEERING PART A-SYSTEMS}, publisher={American Society of Civil Engineers (ASCE)}, author={Ahmed, Ishtiak and Warchol, Shannon and Cunningham, Chris and Rouphail, Nagui}, year={2021}, month={May} }
 @article{fernandes_coelho_rouphail_2020, title={Assessing the impact of closely-spaced intersections on traffic operations and pollutant emissions on a corridor level (vol 54, pg 304, 2017)}, volume={87}, ISSN={["1361-9209"]}, DOI={10.1016/j.trd.2020.102557}, journal={TRANSPORTATION RESEARCH PART D-TRANSPORT AND ENVIRONMENT}, author={Fernandes, P. and Coelho, M. G. and Rouphail, N. M.}, year={2020}, month={Oct} }
 @article{song_kim_williams_rouphail_list_2020, title={Crash Classification by Congestion Type for Highways}, volume={10}, ISSN={["2076-3417"]}, url={https://doi.org/10.3390/app10072583}, DOI={10.3390/app10072583}, abstractNote={Effective management of highway networks requires a thorough understanding of the conditions under which vehicular crashes occur. Such an understanding can and should inform related operational and resource allocation decisions. This paper presents an easily implementable methodology that can classify all reported crashes in terms of the operational conditions under which each crash occurred. The classification methodology uses link-based speed data. Unlike previous secondary collision identification schemes, it neither requires an a priori identification of the precipitating incident nor definition of the precipitating incident’s impact area. To accomplish this objective, the methodology makes use of a novel scheme for distinguishing between recurrent and non-recurrent congestion. A 500-crash case study was performed using a 274 km section of the I-40 in North Carolina. Twelve percent of the case study crashes were classified as occurring in non-recurrent congestion. Thirty-seven percent of the crashes in non-recurrent congestion classified were identified within unreported primary incidents or crashes influence area. The remainder was classified as primary crashes occurring in either uncongested conditions (84%) or recurrent congestion (4%). The methodology can be implemented in any advanced traffic management system for which crash time and link location are available along with corresponding archived link speed data are available.}, number={7}, journal={APPLIED SCIENCES-BASEL}, publisher={MDPI AG}, author={Song, Tai-Jin and Kim, Sangkey and Williams, Billy M. and Rouphail, Nagui M. and List, George F.}, year={2020}, month={Apr} }
 @article{xu_rouphail_aghdashi_ahmed_elefteriadou_2020, title={Modeling Framework for Capacity Analysis of Freeway Segments: Application to Ramp Weaves}, volume={2674}, ISSN={["2169-4052"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85085987562&partnerID=MN8TOARS}, DOI={10.1177/0361198119900157}, abstractNote={ This research proposes a new modeling framework for the analysis of freeway segments. The framework provides a continuum from the operation of ramp weave segments to an equivalent basic segment serving the same traffic with the same number of lanes and free-flow speed. This approach distinguishes between congestion effects caused by high v/c ratios from turbulence caused by merging, diverging, and weaving traffic, thus greatly simplifying the model form, and its extensibility to other freeway segment types. The paper presents an application of this new framework to the analysis of ramp weaves, which were not sufficiently sampled in the development of the HCM6 methodology. The proposed model is shown to be superior to the HCM6 method both in relation to explaining field observations of speeds and in its simplicity in application. The results include a new formula for capacity estimation that is highly sensitive to segment length, and a speed estimation model that converges for low weaving volumes or at very high weaving segment lengths to that observed at a basic segment. Because the proposed model is calibrated with data mostly from North Carolina, it is recommended that data at additional sites be included in a larger calibration effort to ensure its applicability to a broader set of weaving segment configurations. }, number={1}, journal={TRANSPORTATION RESEARCH RECORD}, author={Xu, Dezhong and Rouphail, Nagui M. and Aghdashi, Behzad and Ahmed, Ishtiak and Elefteriadou, Lily}, year={2020}, month={Jan}, pages={148–159} }
 @article{teixeira_macedo_fernandes_bandeira_rouphail_coelho_2019, title={Assessing traffic-related environmental impacts based on different traffic monitoring applications}, volume={37}, ISSN={["2352-1465"]}, DOI={10.1016/j.trpro.2018.12.172}, abstractNote={The objective of this study is to propose a methodological approach to assess the capability of different traffic monitoring applications to estimate emissions generated by road traffic. Global Navigation Satellite Systems and traffic data were collected from different roadways in Portugal and Spain. Emissions were estimated through the Vehicle Specific Power concept, and then, data mining tools were explored to reveal patterns hidden on large amount of data (154 000 sec). Finally, the best relationships between traffic variables and emissions are evaluated. Results show a prediction for CO2 emissions of 99% and 98% to NOX.}, journal={21ST EURO WORKING GROUP ON TRANSPORTATION MEETING (EWGT 2018)}, author={Teixeira, Joao and Macedo, Eloisa and Fernandes, Paulo and Bandeira, Jorge M. and Rouphail, Nagui and Coelho, Margarida C.}, year={2019}, pages={107–114} }
 @article{ahmed_karr_rouphail_chun_tanvir_2019, title={Characterizing Lane Changes via Digitized Infrastructure and Low-Cost GPS}, volume={2673}, ISSN={["2169-4052"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85064917506&partnerID=MN8TOARS}, DOI={10.1177/0361198119841277}, abstractNote={ With the expected increase in the availability of trajectory-level information from connected and autonomous vehicles, issues of lane changing behavior that were difficult to assess with traditional freeway detection systems can now begin to be addressed. This study presents the development and application of a lane change detection algorithm that uses trajectory data from a low-cost GPS-equipped fleet, supplemented with digitized lane markings. The proposed algorithm minimizes the effect of GPS errors by constraining the temporal duration and lateral displacement of a lane change detected using preliminary lane positioning. The algorithm was applied to 637 naturalistic trajectories traversing a long weaving segment and validated through a series of controlled lane change experiments. Analysis of naturalistic trajectory data revealed that ramp-to-freeway trips had the highest number of discretionary lane changes in excess of 1 lane change/vehicle. Overall, excessive lane change rates were highest between the two middle freeway lanes at 0.86 lane changes/vehicle. These results indicate that extreme lane changing behavior may significantly contribute to the peak-hour congestion at the site. The average lateral speed during lane change was 2.7 fps, consistent with the literature, with several freeway–freeway and ramp–ramp trajectories showing speeds up to 7.7 fps. All ramp-to-freeway vehicles executed their first mandatory lane change within 62.5% of the total weaving length, although other weaving lane changes were spread over the entire segment. These findings can be useful for implementing strategies to lessen abrupt and excessive lane changes through better lane pre-positioning. }, number={8}, journal={TRANSPORTATION RESEARCH RECORD}, author={Ahmed, Ishtiak and Karr, Alan and Rouphail, Nagui M. and Chun, Gyounghoon and Tanvir, Shams}, year={2019}, month={Aug}, pages={298–309} }
 @article{ahmed_xu_rouphail_karr_2019, title={Lane Change Rates at Freeway Weaving Sites: Trends in HCM6 and from NGSIM Trajectories}, volume={2673}, ISSN={["2169-4052"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85064555642&partnerID=MN8TOARS}, DOI={10.1177/0361198119841281}, abstractNote={ Concerns have been raised about the HCM6 weaving method’s lack of sensitivity to weaving segment length. This study explores the trends in HCM6 as they relate to lane change estimates and their impact on the segment speed and level of service (LOS). The study also compares HCM6 estimates of lane changes against empirical data from an NGSIM weaving site. Thus, the objectives of this study are twofold: ( a) critically investigate the effect of weaving length on lane change and associated speed model estimates in HCM6, and ( b) analyze trends in lane changes against congestion levels using detailed NGSIM trajectory data, comparing against HCM6 estimates. For ( a) it was found that the lack of sensitivity to weave length is because of the absence of this parameter in the nonweaving lane change and speed models. For ( b), a comparison of HCM6 lane change rates with NGSIM, US-101 data confirmed that the HCM6 estimates for weaving vehicles are fully consistent with those at the NGSIM site, controlling for density. In contrast, nonweaving lane change estimates in HCM6 did not deliver the expected trends, with more discretionary lane changes predicted as congestion increased. Finally, analysis of lane change patterns at the NGSIM site revealed a tendency for early merging for freeway to ramp traffic and uniform merging for ramp to freeway traffic over the length of the weave. Interestingly, a speed analysis showed that in most cases, a higher frequency of discretionary lane changes yielded lower travel times for drivers executing them. }, number={5}, journal={TRANSPORTATION RESEARCH RECORD}, author={Ahmed, Ishtiak and Xu, Dezhong and Rouphail, Nagui and Karr, Alan}, year={2019}, month={May}, pages={627–636} }
 @article{warchol_rouphail_vaughan_kearns_2019, title={Queue-Based Guidance for Signalization Consideration at Two and Three-Legged Intersections}, volume={2673}, ISSN={["2169-4052"]}, DOI={10.1177/0361198119847468}, abstractNote={ This research collected and analyzed gap acceptance in North Carolina to develop a data-driven method for determining the need for considering additional signalization analysis at intersections with fewer than four legs. This method can be used for movements that merge with or cross two lanes of oncoming traffic. It is intended to provide guidance and support to traffic engineers in their decision-making process. Charts are provided to determine the expected 95th percentile queue lengths for left-turn, right-turn, and U-turn movements crossing or merging with two lanes of conflicting traffic. This situation is typically present along four-lane roadways where a one-way primary movement opposes either a minor road right-turn movement or a left-turn movement, or in the case of a median U-turn opening. Adjustment factors to the conflicting flowrate were developed to account for the presence of upstream signalized intersections. This method less frequently recommends further signal consideration when compared with the Manual on Uniform Traffic Control Devices peak hour warrant, but is similar to the delay-based level of service D/E threshold for two-way stop-controlled intersections in HCM6 Chapter 19. }, number={10}, journal={TRANSPORTATION RESEARCH RECORD}, author={Warchol, Shannon and Rouphail, Nagui M. and Vaughan, Chris and Kearns, Brendan}, year={2019}, month={Oct}, pages={416–426} }
 @article{ahmed_rouphail_tanvir_2018, title={Characteristics and Temporal Stability of Recurring Bottlenecks}, volume={2672}, ISSN={["2169-4052"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85060989618&partnerID=MN8TOARS}, DOI={10.1177/0361198118798991}, abstractNote={ This study applies and updates a method which identifies and quantifies the extent of traffic congestion from recurring freeway bottlenecks. Additionally, the spatiotemporal stability of bottlenecks over an extended period was tested. Over time congestion at bottlenecks may increase, may decrease, or may migrate to other nearby locations. Analysis of stability is important since prioritizing and applying treatments at bottlenecks is a multiyear process. In addition, a robust method for selecting sensitivity based parameters to identify and quantify bottleneck effects is presented. Subsequently, a systematic framework is developed for tracking and archiving the spatiotemporal changes in the recurring bottlenecks. The proposed method is demonstrated on a case study on Interstate 40 in North Carolina using three years of probe data. A congestion speed ratio detection threshold of 0.7 and a probability of activation threshold of 33% for the study area were determined from a sensitivity test to ascertain their recurrence. The method identified 13 bottlenecks with their impacts ranging from 35 to 3,278 mi-hours of congestion per year. Eight bottlenecks either newly emerged or had their queues merged or shifted between successive years. Even spatially stable bottlenecks had significant variation in their activation frequency and queue length. Exploration of the changes in bottleneck severity and locations revealed the influence of a long-term work zone in the area and the effect of the rapid growth in traffic demand. Local agencies can use this method to shortlist recurring bottlenecks and track changes to plan mitigation strategies. }, number={42}, journal={TRANSPORTATION RESEARCH RECORD}, author={Ahmed, Ishtiak and Rouphail, Nagui M. and Tanvir, Shams}, year={2018}, month={Dec}, pages={235–246} }
 @article{song_williams_rouphail_2018, title={Data-driven approach for identifying spatiotemporally recurrent bottlenecks}, volume={12}, ISSN={["1751-9578"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85053217294&partnerID=MN8TOARS}, DOI={10.1049/iet-its.2017.0284}, abstractNote={Identification of recurrent bottlenecks is an effective way to hone an appropriate investment in current facilities to relieve congestion. Furthermore, it would enable the ranking or prioritisation of bottlenecks since bottleneck removal and its associated impact alleviation are hampered by limited sources. It is imperative that transportation jurisdiction understand and identify the basis for ranking bottlenecks by exploring: how often they are active; how long it takes the congestion to disappear; and how many miles of road are affected. Previous bottleneck identification schemes have focused on identifying congestion with little attention to distinguishing the recurrent level at the same ‘bottleneck’ location. In contrast to traditional schemes, a data-driven approach for identifying recurrent bottlenecks is introduced, using probe vehicle speed reports. The historical spatiotemporal characteristics of bottlenecks are investigated through a comprehensive analysis of 2253 miles of all state-wide interstates in North Carolina. Using the characteristics determined the recurrent bottleneck locations with a historical time span of bottleneck activation are revealed and tested. The findings of the proposed identification schemes generate critical information in order to quantify and diagnose a bottleneck and its associated impact area.}, number={8}, journal={IET INTELLIGENT TRANSPORT SYSTEMS}, author={Song, Tai-Jin and Williams, Billy M. and Rouphail, Nagui M.}, year={2018}, month={Oct}, pages={756–764} }
 @article{tanvir_frey_rouphail_2018, title={Effect of Light Duty Vehicle Performance on a Driving Style Metric}, volume={2672}, ISSN={["2169-4052"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85060916631&partnerID=MN8TOARS}, DOI={10.1177/0361198118796070}, abstractNote={ Eco-driving involves alterations to driving style to improve energy efficiency. The observed driving style reflects the combined effects of roadway, traffic, driver, and vehicle performance. Although the effect of roadway and traffic characteristics can be inferred from microscale driving activity data, the effect of vehicle performance on driving style is not properly understood. This paper addresses two questions: (1) how different is an individual driver’s driving style when operating vehicles with differences in performance?; and (2) how dissimilar are the driving styles of different drivers when operating vehicles that have similar performance? To answer these questions, we have gathered microscale vehicle activity measurements from 17 controlled real-world driving schedules and two years of naturalistic driving data from five drivers. We also developed a metric for driving style termed “envelope deviation,” which is a distribution of gaps between microscale activity (1 Hz) and fleet average envelope. We found that there is significant inter-driver heterogeneity in driving styles when controlling for vehicle performance. However, no significant inter-vehicle heterogeneity was present in driving styles while controlling for the driver. Findings from this study imply that the choice of vehicle does not significantly alter the natural driving style of a driver. }, number={25}, journal={TRANSPORTATION RESEARCH RECORD}, author={Tanvir, Shams and Frey, H. Christopher and Rouphail, Nagui M.}, year={2018}, month={Dec}, pages={67–78} }
 @article{list_rouphail_smith_williams_2018, title={Reliability Assessment Tool: Development and Prototype Testing}, volume={2672}, ISSN={["2169-4052"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85060926457&partnerID=MN8TOARS}, DOI={10.1177/0361198118798296}, abstractNote={ This paper presents a monitoring system that was developed to assess travel time reliability for observed operating conditions by utilizing traffic stream and non-transportation related data. A prototype was created for an interstate highway route in the Research Triangle region of North Carolina. It describes how the input datasets were obtained, the required data fusion procedures, how the data were analyzed to create the monitoring system outputs, and relevant insights obtained from the reliability monitoring system prototype. }, number={14}, journal={TRANSPORTATION RESEARCH RECORD}, author={List, George F. and Rouphail, Nagui and Smith, Russell and Williams, Billy}, year={2018}, month={Dec}, pages={29–38} }
 @article{yeom_rasdorf_rouphail_schroeder_2018, title={Simulation of Work Zones with Lane Closures in Proximity of Freeway Interchanges}, volume={10}, ISSN={["1941-1197"]}, DOI={10.1109/MITS.2018.2842027}, abstractNote={The paper provides methodologies for microscopic simulation modelling of freeway work zones with lane closures in the proximity of interchanges. In addition, the research presents simulation results using calibrated modelling parameters to determine the capacity available for mainline flow under various operating conditions. The results will help researchers or practitioners with designing and studying freeway work zone sites under various lane configurations using better estimates of delays and queue sizes in the proximity of interchanges. Additionally, a 2 to 1 on-ramp merge condition was explored to predict the merge ratios under both demand and service flow conditions. The paper illustrates how ramp demand affects the share of segment capacity available to mainline traffic to reveal strategies for controlling this demand (via ramp metering for example) in order to maintain a prescribed freeway capacity through the work zone. The overall study result indicates the degree to which the presence of a work zone with lane closures decreases the proportion of mainline flow and shows the degree to which differences in work zone lane configurations affect merge and weave scenarios.}, number={3}, journal={IEEE INTELLIGENT TRANSPORTATION SYSTEMS MAGAZINE}, author={Yeom, Chunho and Rasdorf, William and Rouphail, Nagui and Schroeder, Bastian}, year={2018}, pages={184–195} }
 @article{karmakar_aghdashi_rouphail_williams_2018, title={Validation and Calibration of Freeway Reliability Methodology in the Highway Capacity Manual: Method and Case Studies}, volume={2672}, ISSN={["2169-4052"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85060939515&partnerID=MN8TOARS}, DOI={10.1177/0361198118798723}, abstractNote={ Traffic congestion costs drivers an average of $1,200 a year in wasted fuel and time, with most travelers becoming less tolerant of unexpected delays. Substantial efforts have been made to account for the impact of non-recurring sources of congestion on travel time reliability. The 6th edition of the Highway Capacity Manual (HCM) provides a structured guidance on a step-by-step analysis to estimate reliability performance measures on freeway facilities. However, practical implementation of these methods poses its own challenges. Performing these analyses requires assimilation of data scattered in different platforms, and this assimilation is complicated further by the fact that data and data platforms differ from state to state. This paper focuses on practical calibration and validation methods of the core and reliability analyses described in the HCM. The main objective is to provide HCM users with guidance on collecting data for freeway reliability analysis as well as validating the reliability performance measures predictions of the HCM methodology. A real-world case study on three routes on Interstate 40 in the Raleigh-Durham area in North Carolina is used to describe the steps required for conducting this analysis. The travel time index (TTI) distribution, reported by the HCM models, was found to match those from probe-based travel time data closely up to the 80th percentile values. However, because of a mismatch between the actual and HCM estimated incident allocation patterns both spatially and temporally, and the fact that traffic demands in the HCM methods are by default insensitive to the occurrence of major incidents, the HCM approach tended to generate larger travel time values in the upper regions of the travel time distribution. }, number={15}, journal={TRANSPORTATION RESEARCH RECORD}, author={Karmakar, Nabaruna and Aghdashi, Seyedbehzad and Rouphail, Nagui M. and Williams, Billy M.}, year={2018}, month={Dec}, pages={93–104} }
 @article{rouphail_kim_aghdashi_2017, title={Application of high-resolution vehicle data for free-flow speed estimation}, number={2615}, journal={Transportation Research Record}, author={Rouphail, N. M. and Kim, S. and Aghdashi, S.}, year={2017}, pages={105–112} }
 @article{fernandes_coelho_rouphail_2017, title={Assessing the impact of closely-spaced intersections on traffic operations and pollutant emissions on a corridor level}, volume={54}, ISSN={["1879-2340"]}, DOI={10.1016/j.trd.2017.05.016}, abstractNote={Traffic lights or roundabouts along corridors are usually installed to address location-specific operational needs. An understanding of the impacts on traffic regarding to highly-congested closely-spaced intersections has not been fully addressed. Accordingly, consideration should be given to how these specific segments affect corridor performance as a whole. One mixed roundabout/traffic light/stop-controlled junctions corridor was evaluated with the microscopic traffic model (VISSIM) and emissions methodology (Vehicle Specific Power – VSP). The analysis was focused on two major intersections of the corridor, a roundabout and a traffic light spaced lower than 170 m apart under different traffic demand levels. The traffic data and corridor geometry were coded into VISSIM and compared with an alternative scenario where the traffic light was replaced by a single-lane roundabout. This research also tested a method to improve corridor performance and emissions by examining the integrated effect of the spacing between these intersections on traffic delay and vehicular emissions (carbon dioxide, monoxide carbon, nitrogen oxides, and hydrocarbons). The Fast Non-Dominated Sorting Genetic Algorithm (NSGA-II) was used to find the optimal spacing for these intersections. The analysis showed that the roundabout could achieve lower queue length (∼64%) and emissions (16–27%, depending on the pollutant) than the traffic light. The results also suggested that 200 m of spacing using the best traffic control would provide a moderate advantage in traffic operations and emissions as compared with the existing spacing.}, journal={TRANSPORTATION RESEARCH PART D-TRANSPORT AND ENVIRONMENT}, author={Fernandes, P. and Coelho, M. C. and Rouphail, N. M.}, year={2017}, month={Jul}, pages={304–320} }
 @article{yeom_hajbabaie_rouphail_rasdorf_schroeder_2017, title={Freeway work zone free-flow speed model development}, volume={87}, number={11}, journal={ITE Journal}, author={Yeom, C. and Hajbabaie, A. and Rouphail, N. M. and Rasdorf, W. and Schroeder, B. J.}, year={2017}, pages={38–44} }
 @article{yeom_schroeder_cunningham_salamati_rouphail_2017, title={Lane utilization model development for diverging diamond interchanges}, number={2618}, journal={Transportation Research Record}, author={Yeom, C. and Schroeder, B. J. and Cunningham, C. and Salamati, K. and Rouphail, N. M.}, year={2017}, pages={27–37} }
 @article{li_rouphail_mahmoudi_liu_zhou_2017, title={Multi-scenario optimization approach for assessing the impacts of advanced traffic information under realistic stochastic capacity distributions}, volume={77}, ISSN={["0968-090X"]}, DOI={10.1016/j.trc.2017.01.019}, abstractNote={In this study, to incorporate realistic discrete stochastic capacity distribution over a large number of sampling days or scenarios (say 30–100 days), we propose a multi-scenario based optimization model with different types of traveler knowledge in an advanced traveler information provision environment. The proposed method categorizes commuters into two classes: (1) those with access to perfect traffic information every day, and (2) those with knowledge of the expected traffic conditions (and related reliability measure) across a large number of different sampling days. Using a gap function framework or describing the mixed user equilibrium under different information availability over a long-term steady state, a nonlinear programming model is formulated to describe the route choice behavior of the perfect information (PI) and expected travel time (ETT) user classes under stochastic day-dependent travel time. Driven by a computationally efficient algorithm suitable for large-scale networks, the model was implemented in a standard optimization solver and an open-source simulation package and further applied to medium-scale networks to examine the effectiveness of dynamic traveler information under realistic stochastic capacity conditions.}, journal={TRANSPORTATION RESEARCH PART C-EMERGING TECHNOLOGIES}, author={Li, Mingxin and Rouphail, Nagui M. and Mahmoudi, Monirehalsadat and Liu, Jiangtao and Zhou, Xuesong}, year={2017}, month={Apr}, pages={113–133} }
 @article{li_zhou_rouphail_2017, title={Quantifying travel time variability at a single bottleneck based on stochastic capacity and demand distributions}, volume={21}, ISSN={["1547-2442"]}, DOI={10.1080/15472450.2016.1163639}, abstractNote={ABSTRACT Travel time reliability, an essential factor in traveler route and departure time decisions, serves as an important quality of service measure for dynamic transportation systems. This article investigates a fundamental problem of quantifying travel time variability from its root sources: stochastic capacity and demand variations that follow commonly used log-normal distributions. A volume-to-capacity ratio-based travel time function and a point queue model are used to demonstrate how day-to-day travel time variability can be explained from the underlying demand and capacity variations. One important finding is that closed-form solutions can be derived to formulate travel time variations as a function of random demand/capacity distributions, but there are certain cases in which a closed-form expression does not exist and numerical approximation methods are required. This article also uses probabilistic capacity reduction information to estimate time-dependent travel time variability distributions under conditions of non-recurring traffic congestion. The proposed models provide theoretically rigorous and practically useful tools for understanding the causes of travel time unreliability and evaluating the system-wide benefit of reducing demand and capacity variability.}, number={2}, journal={JOURNAL OF INTELLIGENT TRANSPORTATION SYSTEMS}, author={Li, Mingxin and Zhou, Xuesong and Rouphail, Nagui M.}, year={2017}, pages={79–93} }
 @article{fernandes_salamati_rouphail_coelho_2017, title={The effect of a roundabout corridor's design on selecting the optimal crosswalk location: A multi-objective impact analysis}, volume={11}, ISSN={["1556-8334"]}, DOI={10.1080/15568318.2016.1237689}, abstractNote={ABSTRACT Crosswalks located at mid-block segment between roundabouts can provide a good balance among delay, carbon dioxide (CO2) emissions, and relative difference between vehicles and pedestrians speed. However, when considering local pollutant criteria, the optimal crosswalk location may be different to that obtained for CO2. This paper described a multi-objective analysis of pedestrian crosswalk locations, with the objectives of minimizing delay, emissions, and relative difference between vehicles and pedestrians speed. Accounting for the difference between global (e.g., CO2) and local pollutants (monoxide carbon, nitrogen oxides, and hydrocarbons) was one the main considerations of this work. Vehicle activity along with traffic and pedestrian flows data at six roundabout corridors in Portugal, one in Spain, and one in the United States were collected and extracted. A simulation environment using VISSIM, Vehicle Specific Power, and Surrogate Safety Assessment Model models was used to evaluate traffic operations along the sites. The Fast Non-Dominated Sorting Genetic Algorithm (NSGA-II) was implemented to further search optimal crosswalk locations. The results yielded improvements to both delay and emissions by using site-optimized crosswalks. The findings also revealed that the spacing between intersections widely influenced the optimal crosswalk location along a mid-block section. If the spacing is low (<100 m), the crosswalk location will be approximately in 20%–30% of the spacing length. For spacing values between 140 and 200 m, crosswalks would be located at the midway position. When a specific pollutant criterion was considered, no significant differences were observed among optimal crosswalk data sets.}, number={3}, journal={INTERNATIONAL JOURNAL OF SUSTAINABLE TRANSPORTATION}, author={Fernandes, P. and Salamati, K. and Rouphail, N. M. and Coelho, M. C.}, year={2017}, pages={206–220} }
 @article{fernandes_rouphail_coelho_2017, title={Turboroundabouts along corridors analysis of operational and environmental impacts}, number={2627}, journal={Transportation Research Record}, author={Fernandes, P. and Rouphail, N. M. and Coelho, M. C.}, year={2017}, pages={46–56} }
 @article{kim_hajbabaie_williams_rouphail_2016, title={Dynamic Bandwidth Analysis for Coordinated Arterial Streets}, volume={20}, ISSN={["1547-2442"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84941243905&partnerID=MN8TOARS}, DOI={10.1080/15472450.2015.1074575}, abstractNote={A commonly used strategy for improving mobility along signalized arterials is to coordinate neighboring intersections to minimize vehicle stops by maximizing the duration of green bands, otherwise known as arterial bandwidth. Signal coordination has been researched, developed, and refined for five decades. In lieu of traditional methods that are based on the analysis of programmed green times (which assume all phases operate at their maximum settings), a dynamic bandwidth analysis method is presented that reproduces actual dynamic bandwidth durations using closed loop signal data. The analysis is intended to help assess the performance of semi-actuated coordinated signal systems on arterial streets. In addition, the study highlights the arterial progression benefits that result from changing coordinated intersection offsets based on optimizing the dynamic, rather than the programmed, bandwidths. Detailed analysis at three arterial sites revealed that coordinated green phase time distributions are complex and multimodal and cannot be represented by a single-valued statistic. Dynamic bandwidth analysis confirmed that programmed green bandwidth consistently underestimates the size of the actual dynamic bandwidth, and exhaustive search results highlighted the potential for further improvements in coordination. Future research will include field and simulation comparative studies and the development of efficient methods for dynamic bandwidth optimization.}, number={3}, journal={JOURNAL OF INTELLIGENT TRANSPORTATION SYSTEMS}, author={Kim, Sangkey and Hajbabaie, Ali and Williams, Billy M. and Rouphail, Nagui M.}, year={2016}, pages={294–310} }
 @article{lu_liu_qu_peeta_rouphail_zhou_2016, title={Eco-system optimal time-dependent flow assignment in a congested network}, volume={94}, ISSN={["1879-2367"]}, DOI={10.1016/j.trb.2016.09.015}, abstractNote={This research addresses the eco-system optimal dynamic traffic assignment (ESODTA) problem which aims to find system optimal eco-routing or green routing flows that minimize total vehicular emission in a congested network. We propose a generic agent-based ESODTA model and a simplified queueing model (SQM) that is able to clearly distinguish vehicles’ speed in free-flow and congested conditions for multi-scale emission analysis, and facilitates analyzing the relationship between link emission and delay. Based on the SQM, an expanded space-time network is constructed to formulate the ESODTA with constant bottleneck discharge capacities. The resulting integer linear model of the ESODTA is solved by a Lagrangian relaxation-based algorithm. For the simulation-based ESODTA, we present the column-generation-based heuristic, which requires link and path marginal emissions in the embedded time-dependent least-cost path algorithm and the gradient-projection-based descent direction method. We derive a formula of marginal emission which encompasses the marginal travel time as a special case, and develop an algorithm for evaluating path marginal emissions in a congested network. Numerical experiments are conducted to demonstrate that the proposed algorithm is able to effectively obtain coordinated route flows that minimize the system-wide vehicular emission for large-scale networks.}, journal={TRANSPORTATION RESEARCH PART B-METHODOLOGICAL}, author={Lu, Chung-Cheng and Liu, Jiangtao and Qu, Yunchao and Peeta, Srinivas and Rouphail, Nagui M. and Zhou, Xuesong}, year={2016}, month={Dec}, pages={217–239} }
 @article{hajbabaie_aghdashi_rouphail_2016, title={Enhanced Decision-Making Framework Using Reliability Concepts for Freeway Facilities}, volume={142}, ISSN={0733-947X 1943-5436}, url={http://dx.doi.org/10.1061/(ASCE)TE.1943-5436.0000797}, DOI={10.1061/(ASCE)TE.1943-5436.0000797}, abstractNote={This paper presents a decision-making framework based on a travel time reliability methodology developed under the U.S. Strategic Highway Research Program. Existing methods consider a set of predefined prevailing conditions for the analysis of freeway facilities as the base case. However, a reliability analysis accounts for multiple recurring and nonrecurring congestion sources to estimate the travel time distribution over a long time horizon. This approach considers variations in traffic demand levels, inclement weather conditions, and incidents that occur stochastically on a freeway facility. Several performance measures are defined based on the travel time distribution, which comprehensively cover the full range of operational conditions on the system. Based on the proposed decision-making framework, mobility strategies can be identified, evaluated, and improved.}, number={4}, journal={Journal of Transportation Engineering}, publisher={American Society of Civil Engineers (ASCE)}, author={Hajbabaie, Ali and Aghdashi, Seyedbehzad and Rouphail, Nagui M.}, year={2016}, month={Apr}, pages={04016008} }
 @article{kim_song_rouphail_aghdashi_amaro_goncalves_2016, title={Exploring the association of rear-end crash propensity and micro-scale driver behavior}, volume={89}, ISSN={["1879-1042"]}, DOI={10.1016/j.ssci.2016.05.016}, abstractNote={The relationship between driver behavior at the tactical level and crash experience is a long sought association that has been elusive to explore. The availability of in-vehicle sensing devices capable of capturing and documenting micro-scale dynamic driver behavior offers the opportunity to begin such an exploration. This study integrates rear-end crash data experienced on a 63-mile section of I-40 in North Carolina over a four-year period with three months of micro-scale driving behavioral data gathered by an in-vehicle sensing system (i2D) that records and dispatches second by second vehicle dynamics data to a central database. The information collected by the i2D devices came from a fleet of about 20 vehicles driven by volunteers in their naturalistic driving environment. Additionally all crash and driver data were geo-located onto a link-based GIS environment. The objective of this study is to explore the association of crash propensity and micro-scale driving behavior. The initial findings of this research are promising. First, over 85% of all rear-end crashes occurred on 30 segments extending from 2000 feet upstream of an on-ramp to the on-ramp itself. Secondly, on those segments with high crash rates we have detected a high propensity of drivers to decelerate at high rates (4 m/s2 or more). We have also tested and confirmed that the sharp deceleration phenomenon is not confined to a few drivers, but appears to be common for the high-crash segments, using trip-based analyses.}, journal={SAFETY SCIENCE}, author={Kim, SangKey and Song, Tai-Jin and Rouphail, Nagui M. and Aghdashi, Seyedbehzad and Amaro, Ana and Goncalves, Goncalo}, year={2016}, month={Nov}, pages={45–54} }
 @article{torrao_fontes_coelho_rouphail_2016, title={Integrated indicator to evaluate vehicle performance across: Safety, fuel efficiency and green domains}, volume={92}, ISSN={["1879-2057"]}, DOI={10.1016/j.aap.2016.03.008}, abstractNote={In general, car manufacturers face trade-offs between safety, efficiency and environmental performance when choosing between mass, length, engine power, and fuel efficiency. Moreover, the information available to the consumers makes difficult to assess all these components at once, especially when aiming to compare vehicles across different categories and/or to compare vehicles in the same category but across different model years. The main objective of this research was to develop an integrated tool able to assess vehicle's performance simultaneously for safety and environmental domains, leading to the research output of a Safety, Fuel Efficiency and Green Emissions (SEG) indicator able to evaluate and rank vehicle's performance across those three domains. For this purpose, crash data was gathered in Porto (Portugal) for the period 2006-2010 (N=1374). The crash database was analyzed and crash severity prediction models were developed using advanced logistic regression models. Following, the methodology for the SEG indicator was established combining the vehicle's safety and the environmental evaluation into an integrated analysis. The obtained results for the SEG indicator do not show any trade-off between vehicle's safety, fuel consumption and emissions. The best performance was achieved for newer gasoline passenger vehicles (<5year) with a smaller engine size (<1400cm(3)). According to the SEG indicator, a vehicle with these characteristics can be recommended for a safety-conscious profile user, as well as for a user more interested in fuel economy and/or in green performance. On the other hand, for larger engine size vehicles (>2000cm(3)) the combined score for safety user profile was in average more satisfactory than for vehicles in the smaller engine size group (<1400cm(3)), which suggests that in general, larger vehicles may offer extra protection. The achieved results demonstrate that the developed SEG integrated methodology can be a helpful tool for consumers to evaluate their vehicle selection through different domains (safety, fuel efficiency and green emissions). Furthermore, SEG indicator allows the comparison of vehicles across different categories and vehicle model years. Hence, this research is intended to support the decision-making process for transportation policy, safety and sustainable mobility, providing insights not only to policy makers, but also for general public guidance.}, journal={ACCIDENT ANALYSIS AND PREVENTION}, author={Torrao, G. and Fontes, T. and Coelho, M. and Rouphail, N.}, year={2016}, month={Jul}, pages={153–167} }
 @article{vaughan_jagadish_bharadwaj_cunningham_schroeder_hummer_findley_rouphail_2016, title={Long-term monitoring of wrong-way maneuvers at diverging diamond interchanges}, number={2484}, journal={Transportation Research Record}, author={Vaughan, C. and Jagadish, C. and Bharadwaj, S. and Cunningham, C. M. and Schroeder, B. J. and Hummer, J. E. and Findley, D. and Rouphail, N. M.}, year={2016}, pages={129–139} }
 @article{tanvir_karmakar_rouphail_schroeder_2016, title={Modeling freeway work zones with mesoscopic dynamic traffic simulator validation, gaps, and guidance}, number={2567}, journal={Transportation Research Record}, author={Tanvir, S. and Karmakar, N. and Rouphail, N. M. and Schroeder, B. J.}, year={2016}, pages={122–130} }
 @article{yeom_rouphail_rasdorf_schroeder_2016, title={Simulation guidance for calibration of freeway lane closure capacity}, number={2553}, journal={Transportation Research Record}, author={Yeom, C. and Rouphail, N. M. and Rasdorf, W. and Schroeder, B. J.}, year={2016}, pages={82–89} }
 @article{fernandes_bandeira_fontes_pereira_schroeder_rouphail_coelho_2016, title={Traffic restriction policies in an urban avenue: A methodological overview for a trade-off analysis of traffic and emission impacts using microsimulation}, volume={10}, ISSN={["1556-8334"]}, DOI={10.1080/15568318.2014.885622}, abstractNote={ABSTRACT Urban traffic emissions have been increasing in recent years. To reverse that trend, restrictive traffic measures can be implemented to complement national policies. We have proposed a methodology to assess the impact of three restrictive traffic measures in an urban arterial by using a microsimulation model of traffic and emissions integrated platform. The analysis is extended to some alternative roads and to the overall network area. Traffic restriction measures provided average reductions of 45%, 47%, 35%, and 47% for CO2, CO, NOX, and HC, respectively, due to traffic being diverted to other roads. Nevertheless, increases of 91%, 99%, 55%, and 121% in CO2, CO, NOX, and HC, respectively, can be expected on alternative roads.}, number={3}, journal={INTERNATIONAL JOURNAL OF SUSTAINABLE TRANSPORTATION}, author={Fernandes, Paulo and Bandeira, Jorge M. and Fontes, Tania and Pereira, Sergio Ramos and Schroeder, Bastian J. and Rouphail, Nagui M. and Coelho, Margarida C.}, year={2016}, pages={201–215} }
 @article{fernandes_fontes_neves_pereira_bandeira_rouphail_coelho_2015, title={Assessment of corridors with different types of intersections environmental and traffic performance analysis}, number={2503}, journal={Transportation Research Record}, author={Fernandes, P. and Fontes, T. and Neves, M. and Pereira, S. R. and Bandeira, J. M. and Rouphail, N. M. and Coelho, M. C.}, year={2015}, pages={39–50} }
 @article{aghdashi_hajbabaie_schroeder_trask_rouphail_2015, title={Generating scenarios of freeway reliability analysis hybrid approach}, number={2483}, journal={Transportation Research Record}, author={Aghdashi, S. and Hajbabaie, A. and Schroeder, B. J. and Trask, J. L. and Rouphail, N. M.}, year={2015}, pages={148–159} }
 @article{aghdashi_rouphail_hajbabaie_schroeder_2015, title={Generic speed-flow models for basic freeway segments on general-purpose and managed lanes in undersaturated flow conditions}, number={2483}, journal={Transportation Research Record}, author={Aghdashi, S. and Rouphail, N. M. and Hajbabaie, A. and Schroeder, B. J.}, year={2015}, pages={102–110} }
 @article{fernandes_salamati_rouphail_coelho_2015, title={Identification of emission hotspots in roundabouts corridors}, volume={37}, ISSN={["1361-9209"]}, DOI={10.1016/j.trd.2015.04.026}, abstractNote={Abstract This study describes a methodology to quantify and characterize the vehicular emissions of functionally interdependent roundabouts at a corridor level. Corridor segments include those upstream of each roundabout, the circulating area, downstream of the roundabout as well as midblock sub-segments between adjacent roundabouts. The main purpose of the study is to identify the locations along the corridors where emissions tend to be consistently high. These locations are termed “Emission Hotspots”. The methodology is applied to four existing roundabout corridors in San Diego (California) and Avon (Colorado) in the United States, and in Mealhada and Chaves (Portugal). An extensive sample of second-by-second speed traces is available for these four corridors with roundabouts. The analysis shows that when roundabouts are fairly spaced and have similar geometric design features, no significant differences are observed between emissions of roundabouts located in the corridor. In such cases, the downstream sub-segments are the emission hotspots both in absolute terms (overall contribution on total emissions is higher than 34%) and per unit distance (22% higher than the average corridor value). When roundabouts are unequally spaced the highest emissions hotspots (more than 9% above the average corridor value) are found at the circulating area sub-segments. The results also demonstrate that the entry deflection angle has a slight impact on the spatial distribution of emissions especially in the case of closely spaced roundabouts.}, journal={TRANSPORTATION RESEARCH PART D-TRANSPORT AND ENVIRONMENT}, author={Fernandes, P. and Salamati, K. and Rouphail, N. M. and Coelho, M. C.}, year={2015}, month={Jun}, pages={48–64} }
 @article{yeom_hajbabaie_schroeder_vaughan_xuan_rouphail_2015, title={Innovative work zone capacity models from nationwide field and archival sources}, number={2485}, journal={Transportation Research Record}, author={Yeom, C. and Hajbabaie, A. and Schroeder, B. J. and Vaughan, C. and Xuan, X. Y. and Rouphail, N. M.}, year={2015}, pages={51–60} }
 @article{zhou_tanvir_lei_taylor_liu_rouphail_frey_2015, title={Integrating a simplified emission estimation model and mesoscopic dynamic traffic simulator to efficiently evaluate emission impacts of traffic management strategies}, volume={37}, ISSN={["1361-9209"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84941658996&partnerID=MN8TOARS}, DOI={10.1016/j.trd.2015.04.013}, abstractNote={This paper presents a computationally efficient and theoretically rigorous dynamic traffic assignment (DTA) model and its solution algorithm for a number of emerging emissions and fuel consumption related applications that require both effective microscopic and macroscopic traffic stream representations. The proposed model embeds a consistent cross-resolution traffic state representation based on Newell’s simplified kinematic wave and linear car following models. Tightly coupled with a computationally efficient emission estimation package MOVES Lite, a mesoscopic simulation-based dynamic network loading framework DTALite is adapted to evaluate traffic dynamics and vehicle emission/fuel consumption impact of different traffic management strategies.}, journal={TRANSPORTATION RESEARCH PART D-TRANSPORT AND ENVIRONMENT}, author={Zhou, Xuesong and Tanvir, Shams and Lei, Hao and Taylor, Jeffrey and Liu, Bin and Rouphail, Nagui M. and Frey, H. Christopher}, year={2015}, month={Jun}, pages={123–136} }
 @article{vaughan_jagadish_bharadwaj_cunningham_schroeder_hummer_findley_rouphail_2015, title={Long-term monitoring of wrong-way maneuvers at diverging diamond interchanges}, number={2484}, journal={Transportation Research Record}, author={Vaughan, C. and Jagadish, C. and Bharadwaj, S. and Cunningham, C. M. and Schroeder, B. J. and Hummer, J. E. and Findley, D. and Rouphail, N. M.}, year={2015}, pages={129–139} }
 @article{taylor_zhou_rouphail_porter_2015, title={Method for investigating intradriver heterogeneity using vehicle trajectory data: A Dynamic Time Warping approach}, volume={73}, ISSN={["0191-2615"]}, DOI={10.1016/j.trb.2014.12.009}, abstractNote={After first extending Newell’s car-following model to incorporate time-dependent parameters, this paper describes the Dynamic Time Warping (DTW) algorithm and its application for calibrating this microscopic simulation model by synthesizing driver trajectory data. Using the unique capabilities of the DTW algorithm, this paper attempts to examine driver heterogeneity in car-following behavior, as well as the driver’s heterogeneous situation-dependent behavior within a trip, based on the calibrated time-varying response times and critical jam spacing. The standard DTW algorithm is enhanced to address a number of estimation challenges in this specific application, and a numerical experiment is presented with vehicle trajectory data extracted from the Next Generation Simulation (NGSIM) project for demonstration purposes. The DTW algorithm is shown to be a reasonable method for processing large vehicle trajectory datasets, but requires significant data reduction to produce reasonable results when working with high resolution vehicle trajectory data. Additionally, singularities present an interesting match solution set to potentially help identify changing driver behavior; however, they must be avoided to reduce analysis complexity.}, journal={TRANSPORTATION RESEARCH PART B-METHODOLOGICAL}, author={Taylor, Jeffrey and Zhou, Xuesong and Rouphail, Nagui M. and Porter, Richard J.}, year={2015}, month={Mar}, pages={59–80} }
 @article{fernandes_fontes_pereira_rouphail_coelho_2015, title={Multicriteria assessment of crosswalk location in urban roundabout corridors}, number={2517}, journal={Transportation Research Record}, author={Fernandes, P. and Fontes, T. and Pereira, S. R. and Rouphail, N. M. and Coelho, M. C.}, year={2015}, pages={37–47} }
 @article{list_yang_rouphail_2015, title={On the Treatment of Trucks for Analysis of Freeway Capacity}, ISSN={["2169-4052"]}, DOI={10.3141/2483-14}, abstractNote={ The influence of trucks on highway performance has always been of interest. However, planning studies today tend to assume that a certain percentage of the traffic stream is trucks (e.g., 5%) and to make adjustments accordingly. The Highway Capacity Manual (HCM) converts trucks into passenger car equivalents by using a passenger car equivalent factor. For the HCM, however, this situation is changing. This paper describes changes to the basic freeway section methodology that are being developed to better address truck-related issues. Specifically, new models predict the space mean speeds of autos and trucks in mixed traffic streams for a variety of road grades. Also presented is a capacity adjustment factor that allows conversion of capacity values for auto-only conditions to be transformed into equivalent capacity values for mixed traffic conditions. The methodologies are presented, their development is described, and examples are given to illustrate how the procedure works. }, number={2483}, journal={TRANSPORTATION RESEARCH RECORD}, author={List, George F. and Yang, Bo and Rouphail, Nagui M.}, year={2015}, pages={120–129} }
 @article{hajbabaie_rouphail_schroeder_dowling_2015, title={Planning-level methodology for freeway facilities}, number={2483}, journal={Transportation Research Record}, author={Hajbabaie, A. and Rouphail, N. M. and Schroeder, B. J. and Dowling, R.}, year={2015}, pages={47–56} }
 @article{mamidipalli_sisiopiku_schroeder_elefteriadou_salamati_rouphail_2015, title={Probit-based pedestrian gap acceptance model for midblock crossing locations}, number={2519}, journal={Transportation Research Record}, author={Mamidipalli, S. V. and Sisiopiku, V. P. and Schroeder, B. J. and Elefteriadou, L. and Salamati, K. and Rouphail, N. M.}, year={2015}, pages={128–136} }
 @article{salamati_rouphail_frey_liu_schroeder_2015, title={Simplified method for comparing emissions in roundabouts and at signalized intersections}, number={2517}, journal={Transportation Research Record}, author={Salamati, K. and Rouphail, N. M. and Frey, H. C. and Liu, B. and Schroeder, B. J.}, year={2015}, pages={48–60} }
 @article{anya_rouphail_frey_schroeder_2014, title={Application of AIMSUN microsimulation model to estimate emissions on signalized arterial corridors}, number={2428}, journal={Transportation Research Record}, author={Anya, A. R. and Rouphail, N. M. and Frey, H. C. and Schroeder, B.}, year={2014}, pages={75–86} }
 @article{bandeira_carvalho_khattak_rouphail_fontes_fernandes_pereira_coelho_2014, title={Empirical assessment of route choice impact on emissions over different road types, traffic demands, and driving scenarios}, volume={10}, ISSN={1556-8318 1556-8334}, url={http://dx.doi.org/10.1080/15568318.2014.901447}, DOI={10.1080/15568318.2014.901447}, abstractNote={ABSTRACT Eco-routing has been shown as a promising strategy to reduce emissions. However, during peak periods, with limited additional capacity, the eco-friendliness of various routes may change. We have explored this issue empirically by covering about 13,300 km, in three different areas, using GPS-equipped vehicles to record second-by-second vehicle dynamics. This study has confirmed the importance of the eco-routing concept given that the selection of eco-friendly routes can lead to significant emissions savings. Furthermore, these savings are expected to be practically unchanged during the peak period. However, some potential negative externalities may arise from purely dedicated eco-friendly navigation systems.}, number={3}, journal={International Journal of Sustainable Transportation}, publisher={Informa UK Limited}, author={Bandeira, Jorge M. and Carvalho, Dário O. and Khattak, Asad J. and Rouphail, Nagui M. and Fontes, Tânia and Fernandes, Paulo and Pereira, Sérgio R. and Coelho, Margarida C.}, year={2014}, month={Nov}, pages={271–283} }
 @article{yeom_schroeder_cunningham_vaughan_rouphail_hummer_2014, title={Lane utilization at two-lane arterial approaches to double crossover diamond interchanges}, number={2461}, journal={Transportation Research Record}, author={Yeom, C. and Schroeder, B. J. and Cunningham, C. and Vaughan, C. and Rouphail, N. M. and Hummer, J. E.}, year={2014}, pages={103–112} }
 @article{tarrao_coelho_rouphail_2014, title={Modeling the impact of subject and opponent vehicles on crash severity in two-vehicle collisions}, number={2432}, journal={Transportation Research Record}, author={Tarrao, G. A. and Coelho, M. C. and Rouphail, N. M.}, year={2014}, pages={53–64} }
 @article{schroeder_rouphail_aghdashi_2013, title={Deterministic framework and methodology for evaluating travel time reliability on freeway facilities}, number={2396}, journal={Transportation Research Record}, author={Schroeder, B. J. and Rouphail, N. M. and Aghdashi, S.}, year={2013}, pages={61–70} }
 @article{xu_williams_rouphail_chase_2013, title={Development of an oversaturated speed-flow model based on the highway capacity manual}, number={2395}, journal={Transportation Research Record}, author={Xu, Y. L. and Williams, B. M. and Rouphail, N. M. and Chase, R. T.}, year={2013}, pages={41–48} }
 @article{salamati_coelho_fernandes_rouphail_frey_bandeira_2013, title={Emissions estimation at multilane roundabouts effects of movement and approach lane}, number={2389}, journal={Transportation Research Record}, author={Salamati, K. and Coelho, M. C. and Fernandes, P. J. and Rouphail, N. M. and Frey, H. C. and Bandeira, J.}, year={2013}, pages={12–21} }
 @article{sajjadi_schroeder_rouphail_2013, title={Enhancements to the freeway facilities method in the highway capacity manual to enable reliability analysis}, number={2395}, journal={Transportation Research Record}, author={Sajjadi, S. and Schroeder, B. and Rouphail, N. M.}, year={2013}, pages={21–30} }
 @article{aghdashi_rouphail_hajbabaie_2013, title={Estimation of incident propensity for reliability analysis in the highway capacity manual}, number={2395}, journal={Transportation Research Record}, author={Aghdashi, S. and Rouphail, N. M. and Hajbabaie, A.}, year={2013}, pages={123–131} }
 @article{salamati_schroeder_geruschat_rouphail_2013, title={Event-based modeling of driver yielding behavior to pedestrians at two-lane roundabout approaches}, number={2389}, journal={Transportation Research Record}, author={Salamati, K. and Schroeder, B. J. and Geruschat, D. R. and Rouphail, N. M.}, year={2013}, pages={1–11} }
 @article{bugg_rouphail_schroeder_2013, title={Lane Choice Model for Signalized Intersections with an Auxiliary Through Lane}, volume={139}, ISSN={["1943-5436"]}, DOI={10.1061/(asce)te.1943-5436.0000513}, abstractNote={AbstractAn auxiliary through lane (ATL) is a commonly used congestion relief measure at signalized intersections in which fiscal and right-of-way constraints do not allow for full widening between intersections. Previously developed models have predicted the flow in the ATL as a function of macroscopic elements, such as through-movement demand and the ratio of average green time to cycle length. However, these models explain neither driver behavior nor motivation to use the ATL, nor can such an approach be used in microscopic simulation models. This paper presents empirically developed models for driver lane choice at signalized intersection approaches with one ATL and one continuous through lane (CTL). These models were developed from a calibration data set that covers eight ATL approaches in three U.S. states, for a total of 12 h of observation. The results suggest that the utility of the ATL is a function of each through-movement driver’s arrival time (during either the effective red or green phase), a...}, number={4}, journal={JOURNAL OF TRANSPORTATION ENGINEERING}, author={Bugg, Zachary and Rouphail, Nagui M. and Schroeder, Bastian}, year={2013}, month={Apr}, pages={371–378} }
 @article{huntsinger_rouphail_2013, title={Temporal stability of generation choice models}, number={2344}, journal={Transportation Research Record}, author={Huntsinger, L. F. and Rouphail, N. M.}, year={2013}, pages={79–87} }
 @article{huntsinger_rouphail_bloomfield_2013, title={Trip Generation Models Using Cumulative Logistic Regression}, volume={139}, ISSN={["0733-9488"]}, DOI={10.1061/(asce)up.1943-5444.0000151}, abstractNote={This paper evaluates the usefulness of the cumulative logistic regression model for estimating trip generation. The cumulative logistic regression model is a type of discrete choice model that estimates relationships between an ordered dependent variable, for example, person trip generation, and a set of independent variables, for example, household size, income, and workers. In addition to testing the model form, life cycle, area type, and accessibility variables are evaluated along with a set of widely used explanatory variables. A secondary focus of this paper is on the issue of temporal stability. Temporal stability is concerned with how models developed during one period of time transfer to a future period. The evaluation includes models based on widely used explanatory variables in addition to models supplemented with life cycle, area type, and accessibility variables to evaluate whether these variables result in improved stability. Analysis includes models estimated using 1995 survey data, applied using 2006 socioeconomic data, and evaluated against 2006 observed data. The results of this analysis show that cumulative logistic regression models are good candidate models for estimating trip generation and for improving the temporal stability of the model results. With respect to life cycle, area type, and accessibility, this research shows that there is benefit in including these variables to help explain trip making and to improve temporal stability.}, number={3}, journal={JOURNAL OF URBAN PLANNING AND DEVELOPMENT}, author={Huntsinger, Leta F. and Rouphail, Nagui M. and Bloomfield, Peter}, year={2013}, month={Sep}, pages={176–184} }
 @article{liu_wang_schroeder_rouphail_2012, title={An analytical framework for managed lane facility performance evaluation}, volume={82}, number={10}, journal={ITE Journal}, author={Liu, X. C. and Wang, Y. H. and Schroeder, B. J. and Rouphail, N. M.}, year={2012}, pages={30–36} }
 @article{chase_williams_rouphail_kim_2012, title={Comparative Evaluation of Reported Speeds from Corresponding Fixed-Point and Probe-Based Detection Systems}, ISSN={["0361-1981"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84874037734&partnerID=MN8TOARS}, DOI={10.3141/2308-12}, abstractNote={ Point-based traffic sensors, such as microwave radar and acoustic sensors, provide the valuable capability of sampling the entire traffic stream. However, full network coverage with point sensors requires a significant initial capital investment and ongoing maintenance expenditures. Probe-based sensors can cover an extensive roadway network at a much lower cost because roadway-based field equipment is not required. Decisions regarding the relative level of point sensor- versus probe-based deployment for traffic monitoring involve evaluating the trade-off between the value of comprehensive detection versus total system costs. An essential step in evaluating this trade-off involves directly comparing collocated point sensor and probe vehicle systems to understand how the derived traffic stream measures from the two approaches differ. This study compared 5-min speeds from microwave radar and acoustic sensors with link speeds from Global Positioning System (GPS) probes for both directions at five freeway locations. Systematic differences were found at one location. Floating car GPS runs were performed to confirm that the systematic error lay in the point speeds. The speed differences at all sites were normally distributed, with three locations indicating a mean speed difference greater than 5 mph. Nonsystematic speed differences were identified; the difference was more than 1.5 standard deviations lower than the mean difference. This difference may indicate inherent inaccuracies in reported GPS speeds under heavy congestion, including instances of time lag in recovering from congested speeds. }, number={2308}, journal={TRANSPORTATION RESEARCH RECORD}, author={Chase, R. Thomas and Williams, Billy M. and Rouphail, Nagui M. and Kim, SangKey}, year={2012}, pages={110–119} }
 @article{schroeder_rouphail_salamati_bugg_2012, title={Effect of pedestrian impedance on vehicular capacity at multilane roundabouts with consideration of crossing treatments}, number={2312}, journal={Transportation Research Record}, author={Schroeder, B. and Rouphail, N. M. and Salamati, K. and Bugg, Z.}, year={2012}, pages={14–24} }
 @article{bandeira_almeida_khattak_rouphail_coelho_2012, title={Generating Emissions Information for Route Selection: Experimental Monitoring and Routes Characterization}, volume={17}, ISSN={1547-2450 1547-2442}, url={http://dx.doi.org/10.1080/15472450.2012.706197}, DOI={10.1080/15472450.2012.706197}, abstractNote={Infrastructure and traffic management technologies can have substantial impact on fuel use and emissions. This article explores a way to generate information about emissions and other route characteristics for drivers faced with a choice of routes. Global positioning system (GPS)-equipped vehicles were used to traverse various paths between origins and destinations to collect second-by-second trajectory data required for microscale emission analysis. A methodology based on the vehicle specific power (VSP) concept was used to estimate the emissions impact. On-board video footage recorded route features, traffic incidents, and congestion levels. Two different vehicles and drivers traversed several urban and intercity routes to enable the consideration of the influence of driver behavior and vehicle dynamics. It was found that the choice of a route can substantially affect emission rates of the analysed pollutants and that smoother driving styles can also result in considerable emissions reduction. A trade-off between reducing CO2/fuel consumption and local pollutants has been identified. Specifically, faster intercity routes are more desirable in terms of fuel use and CO2 emissions. However, these same routes yielded carbon monoxide, nitrous oxides, and hydrocarbons emission increases of up to 150%. These findings have implications for future investment and policy decisions regarding eco routing strategies.}, number={1}, journal={Journal of Intelligent Transportation Systems}, publisher={Informa UK Limited}, author={Bandeira, Jorge and Almeida, Tiago G. and Khattak, Asad J. and Rouphail, Nagui M. and Coelho, Margarida C.}, year={2012}, month={Oct}, pages={3–17} }
 @article{bugg_rouphail_schroeder_2012, title={Guidance for simulation-based modeling of auxiliary through lanes}, number={2311}, journal={Transportation Research Record}, author={Bugg, Z. and Rouphail, N. M. and Schroeder, B.}, year={2012}, pages={51–58} }
 @article{liu_wang_schroeder_rouphail_2012, title={Quantifying cross-weave impact on capacity reduction for freeway facilities with managed lanes}, number={2278}, journal={Transportation Research Record}, author={Liu, X. C. and Wang, Y. H. and Schroeder, B. J. and Rouphail, N. M.}, year={2012}, pages={171–179} }
 @article{salamati_schroeder_rouphail_cunningham_zhang_kaber_2012, title={Simulator study of driver responses to pedestrian treatments at multilane roundabouts}, number={2312}, journal={Transportation Research Record}, author={Salamati, K. and Schroeder, B. and Rouphail, N. M. and Cunningham, C. and Zhang, Y. and Kaber, D.}, year={2012}, pages={67–75} }
 @article{liu_williams_rouphail_2012, title={Temporal stability of freeway macroscopic traffic stream models}, number={2315}, journal={Transportation Research Record}, author={Liu, C. H. and Williams, B. M. and Rouphail, N. M.}, year={2012}, pages={131–140} }
 @article{jia_zhou_rouphail_2012, title={Traffic mobility impact of mileage-based user fees on traveler route choice behavior and network performance planning-level traffic equilibrium-based approach}, number={2302}, journal={Transportation Research Record}, author={Jia, A. and Zhou, X. S. and Rouphail, N. M.}, year={2012}, pages={164–173} }
 @article{huntsinger_rouphail_2012, title={Value of life cycle in explaining trip-making behavior and improving temporal stability of trip generation models}, number={2322}, journal={Transportation Research Record}, author={Huntsinger, L. F. and Rouphail, N. M.}, year={2012}, pages={60–69} }
 @article{kittelson_rouphail_williams_zhou_2011, title={Analyzing operational improvements as an alternative to traditional highway construction}, number={2223}, journal={Transportation Research Record}, author={Kittelson, W. K. and Rouphail, N. M. and Williams, B. M. and Zhou, X. S.}, year={2011}, pages={18–25} }
 @article{huntsinger_rouphail_2011, title={Bottleneck and queuing analysis calibrating volume-delay functions of travel demand models}, number={2255}, journal={Transportation Research Record}, author={Huntsinger, L. F. and Rouphail, N. M.}, year={2011}, pages={117–124} }
 @article{salamati_schroeder_rouphail_cunningham_long_barlow_2011, title={Development and implementation of conflict-based assessment of pedestrian safety to evaluate accessibility of complex intersections}, number={2264}, journal={Transportation Research Record}, author={Salamati, K. and Schroeder, B. and Rouphail, N. M. and Cunningham, C. and Long, R. and Barlow, J.}, year={2011}, pages={148–155} }
 @article{zhai_frey_rouphail_2011, title={Development of a modal emissions model for a hybrid electric vehicle}, volume={16}, ISSN={["1361-9209"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-79957940661&partnerID=MN8TOARS}, DOI={10.1016/j.trd.2011.05.001}, abstractNote={With the growing market share of hybrid electric vehicles (HEVs), new methods are needed for estimating their actual energy use and emissions in order to support emission inventories. This research quantifies criteria associated with startup and shutdown of the internal combustion engine (ICE) for a 2001 Toyota Prius HEV and develops a modal tailpipe emissions model under hot stabilized conditions. The engine is found to be “off” below thresholds of engine power demand that are speed and acceleration dependent. Vehicle specific power (VSP) is used as the basis for modeling emissions. The predicted cycle emissions of CO, NOx and HC for individual cycles are subject to large relative errors, but the overall emission predictions for the average of multiple cycles have relative errors within 10% for each selected pollutant. The ICE engine status identification method is recommended for application to model HEV emissions under actual driving conditions.}, number={6}, journal={TRANSPORTATION RESEARCH PART D-TRANSPORT AND ENVIRONMENT}, author={Zhai, Haibo and Frey, H. Christopher and Rouphail, Nagui M.}, year={2011}, month={Aug}, pages={444–450} }
 @article{schroeder_rouphail_2011, title={Empirical Behavioral Models to Support Alternative Tools for the Analysis of Mixed-Priority Pedestrian-Vehicle Interaction in a Highway Capacity Context}, volume={16}, ISSN={1877-0428}, url={http://dx.doi.org/10.1016/j.sbspro.2011.04.485}, DOI={10.1016/j.sbspro.2011.04.485}, abstractNote={This paper presents behavioral-based models for describing pedestrian gap acceptance at unsignalized crosswalks in a mixed-priority environment, where some drivers yield and some pedestrians cross in gaps. Logistic regression models are developed to predict the probability of pedestrian crossings as a function of vehicle dynamics, pedestrian assertiveness, and other factors. In combination with prior work on probabilistic yielding models, the results can be incorporated in a simulation environment, where they can more fully describe the interaction of these two modes. The approach is intended to supplement HCM analytical procedure for locations where significant interaction occurs between drivers and pedestrians, including modern roundabouts.}, journal={Procedia - Social and Behavioral Sciences}, publisher={Elsevier BV}, author={Schroeder, Bastian J. and Rouphail, Nagui M.}, year={2011}, pages={653–663} }
 @article{schroeder_rouphail_2011, title={Event-Based Modeling of Driver Yielding Behavior at Unsignalized Crosswalks}, volume={137}, ISSN={["1943-5436"]}, DOI={10.1061/(asce)te.1943-5436.0000225}, abstractNote={This research explores factors associated with driver yielding behavior at unsignalized pedestrian crossings and develops predictive models for yielding using logistic regression. It considers the effect of variables describing driver attributes, pedestrian characteristics and concurrent conditions at the crosswalk on the yield response. Special consideration is given to 'vehicle dynamics constraints' that form a threshold for the potential to yield. Similarities are identified to driver reaction in response to the 'amber' indication at a signalized intersection. The logit models were developed from data collected at two unsignalized mid-block crosswalks in North Carolina. The data include 'before' and 'after' observations of two pedestrian safety treatments, an in-street pedestrian crossing sign and pedestrian-actuated in-roadway warning lights.The analysis suggests that drivers are more likely to yield to assertive pedestrians who walk briskly in their approach to the crosswalk. In turn, the yield probability is reduced with higher speeds, deceleration rates and if vehicles are traveling in platoons. The treatment effects proved to be significant and increased the propensity of drivers to yield, but their effectiveness may be dependent on whether the pedestrian activates the treatment.The results of this research provide new insights on the complex interaction of pedestrians and vehicles at unsignalized intersections and have implications for future work towards predictive models for driver yielding behavior. The developed logit models can provide the basis for representing driver yielding behavior in a microsimulation modeling environment.}, number={7}, journal={JOURNAL OF TRANSPORTATION ENGINEERING}, author={Schroeder, Bastian J. and Rouphail, Nagui M.}, year={2011}, month={Jul}, pages={455–465} }
 @article{reynolds_rouphail_zhou_2011, title={Turn pocket blockage and spillback models applications for signal timing and capacity analysis}, number={2259}, journal={Transportation Research Record}, author={Reynolds, W. L. and Rouphail, N. M. and Zhou, X. S.}, year={2011}, pages={112–122} }
 @article{schroeder_rouphail_2010, title={Estimating operational impacts of freeway work zones on extended facilities}, number={2169}, journal={Transportation Research Record}, author={Schroeder, B. J. and Rouphail, N. M.}, year={2010}, pages={70–80} }
 @article{reynolds_zhou_rouphail_li_2010, title={Estimating sustained service rates at signalized intersections with short left-turn pockets mesoscopic approach}, number={2173}, journal={Transportation Research Record}, author={Reynolds, W. L. and Zhou, X. S. and Rouphail, N. M. and Li, M. X.}, year={2010}, pages={64–71} }
 @article{jia_williams_rouphail_2010, title={Identification and calibration of site-specific stochastic freeway breakdown and queue discharge}, number={2188}, journal={Transportation Research Record}, author={Jia, A. and Williams, B. M. and Rouphail, N. M.}, year={2010}, pages={148–155} }
 @article{schroeder_rouphail_2010, title={Mixed-priority pedestrian delay models at single-lane roundabouts}, number={2182}, journal={Transportation Research Record}, author={Schroeder, B. J. and Rouphail, N. M.}, year={2010}, pages={129–138} }
 @article{mei_hu_rouphail_lee_2010, title={Simulation model for studying impact of vehicle-to-vehicle wireless communications on traffic network operations}, number={2189}, journal={Transportation Research Record}, author={Mei, B. and Hu, H. J. and Rouphail, N. M. and Lee, J. J.}, year={2010}, pages={107–115} }
 @article{frey_zhang_rouphail_2010, title={Vehicle-Specific Emissions Modeling Based upon on-Road Measurements}, volume={44}, ISSN={["1520-5851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-77951826102&partnerID=MN8TOARS}, DOI={10.1021/es902835h}, abstractNote={Vehicle-specific microscale fuel use and emissions rate models are developed based upon real-world hot-stabilized tailpipe measurements made using a portable emissions measurement system. Consecutive averaging periods of one to three multiples of the response time are used to compare two semiempirical physically based modeling schemes. One scheme is based on internally observable variables (IOVs), such as engine speed and manifold absolute pressure, while the other is based on externally observable variables (EOVs), such as speed, acceleration, and road grade. For NO, HC, and CO emission rates, the average R(2) ranged from 0.41 to 0.66 for the former and from 0.17 to 0.30 for the latter. The EOV models have R(2) for CO(2) of 0.43 to 0.79 versus 0.99 for the IOV models. The models are sensitive to episodic events in driving cycles such as high acceleration. Intervehicle and fleet average modeling approaches are compared; the former account for microscale variations that might be useful for some types of assessments. EOV-based models have practical value for traffic management or simulation applications since IOVs usually are not available or not used for emission estimation.}, number={9}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Frey, H. Christopher and Zhang, Kaishan and Rouphail, Nagui M.}, year={2010}, month={May}, pages={3594–3600} }
 @article{coelho_farias_rouphail_2009, title={A Numerical Tool for Estimating Pollutant Emissions and Vehicles Performance in Traffic Interruptions on Urban Corridors}, volume={3}, ISSN={["1556-8334"]}, DOI={10.1080/15568310802175641}, abstractNote={ABSTRACT The principal objective of this research was to develop and apply a traffic and emission decision support (TEDS) tool to urban highway corridors. This model simulates traffic while predicting time elapsed, energy consumed, and pollutants emitted to the atmosphere by vehicles on the corridor. Because emissions from internal combustion engines are very high during speed-change cycles, congested stop-and-go traffic can be very detrimental to local levels of pollution. Thus, the research was mainly focused on the existence and quantification of effects for local singularities (or traffic interruptions), such as pay tolls, roundabouts, and traffic signals within the corridor. This approach yielded a numerical predictive model, based on experimental measurements and concepts of traffic flow theory, which explains the interaction between the system operational variables of each traffic interruption and the environmental and traffic performance variables. In particular, the focus was on carbon monoxide, carbon dioxide, nitric oxide, and hydrocarbons emissions and their relation to queue length and stops. The proposed traffic and emission estimation models provide an overall pollution estimate for a traffic interruption under any control configuration and traffic demand pattern.}, number={4}, journal={INTERNATIONAL JOURNAL OF SUSTAINABLE TRANSPORTATION}, author={Coelho, Margarida C. and Farias, Tiago L. and Rouphail, Nagui M.}, year={2009}, pages={246–262} }
 @article{coelho_frey_rouphail_zhai_pelkmans_2009, title={Assessing methods for comparing emissions from gasoline and diesel light-duty vehicles based on microscale measurements}, volume={14}, ISSN={["1361-9209"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-58849133274&partnerID=MN8TOARS}, DOI={10.1016/j.trd.2008.11.005}, abstractNote={This paper assess whether a real-world second-by-second methodology that integrates vehicle activity and emissions rates for light-duty gasoline vehicles can be extended to diesel vehicles. Secondly it compares fuel use and emission rates between gasoline and diesel light-duty vehicles. To evaluate the methodology, real-world field data from two light-duty diesel vehicles are used. Vehicle specific power, a function of vehicle speed, acceleration, and road grade, is evaluated with respect to ability to explain variation in emissions rates. Vehicle specific power has been used previously to define activity-based modes and to quantify variation in fuel use and emission rates of gasoline vehicles taking into account idle, acceleration, cruise, and deceleration. The fuel use and emission rates for light-duty diesel vehicles can also be explained using vehicle specific power -based modes. Thus, the methodology enables direct comparisons for different vehicle fuels and technologies. Furthermore, the method can be used to estimate average fuel use and emission rates for a wide variety of driving cycles.}, number={2}, journal={TRANSPORTATION RESEARCH PART D-TRANSPORT AND ENVIRONMENT}, author={Coelho, Margarida C. and Frey, H. Christopher and Rouphail, Nagui M. and Zhai, Haibo and Pelkmans, Luc}, year={2009}, month={Mar}, pages={91–99} }
 @article{zhai_frey_rouphail_goncalves_farias_2009, title={Comparison of Flexible Fuel Vehicle and Life-Cycle Fuel Consumption and Emissions of Selected Pollutants and Greenhouse Gases for Ethanol 85 Versus Gasoline}, volume={59}, ISSN={["1096-2247"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-70350516518&partnerID=MN8TOARS}, DOI={10.3155/1047-3289.59.8.912}, abstractNote={Abstract The objective of this research is to evaluate differences in fuel consumption and tailpipe emissions of flexible fuel vehicles (FFVs) operated on ethanol 85 (E85) versus gasoline. Theoretical ratios of fuel consumption and carbon dioxide (CO2) emissions for both fuels are estimated based on the same amount of energy released. Second-by-second fuel consumption and emissions from one FFV Ford Focus fueled with E85 and gasoline were measured under real-world traffic conditions in Lisbon, Portugal, using a portable emissions measurement system (PEMS). Cycle average dynamometer fuel consumption and emission test results for FFVs are available from the U.S. Department of Energy, and emissions certification test results for ethanol-fueled vehicles are available from the U.S. Environmental Protection Agency. On the basis of the PEMS data, vehicle-specific power (VSP)-based modal average fuel and emission rates for both fuels are estimated. For E85 versus gasoline, empirical ratios of fuel consumption and CO2 emissions agree within a margin of error to the theoretical expectations. Carbon monoxide (CO) emissions were found to be typically lower. From the PEMS data, nitric oxide (NO) emissions associated with some higher VSP modes are higher for E85. From the dynamometer and certification data, average hydrocarbon (HC) and nitrogen oxides (NOx) emission differences vary depending on the vehicle. The differences of average E85 versus gasoline emission rates for all vehicle models are −22% for CO, 12% for HC, and −8% for NOx emissions, which imply that replacing gasoline with E85 reduces CO emissions, may moderately decrease NOx tailpipe emissions, and may increase HC tailpipe emissions. On a fuel life cycle basis for corn-based ethanol versus gasoline, CO emissions are estimated to decrease by 18%. Life-cycle total and fossil CO2 emissions are estimated to decrease by 25 and 50%, respectively; however, life-cycle HC and NOx emissions are estimated to increase by 18 and 82%, respectively.}, number={8}, journal={JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION}, author={Zhai, Haibo and Frey, H. Christopher and Rouphail, Nagui M. and Goncalves, Goncalo A. and Farias, Tiago L.}, year={2009}, month={Aug}, pages={912–924} }
 @article{hu_williams_rouphail_khattak_zhou_2009, title={Modeling the role of transportation information in mitigating major capacity reductions in a regional network}, number={2138}, journal={Transportation Research Record}, author={Hu, H. J. and Williams, B. M. and Rouphail, N. M. and Khattak, A. J. and Zhou, X. S.}, year={2009}, pages={75–84} }
 @article{frey_zhai_rouphail_2009, title={Regional On-Road Vehicle Running Emissions Modeling and Evaluation for Conventional and Alternative Vehicle Technologies}, volume={43}, ISSN={["1520-5851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-70350776818&partnerID=MN8TOARS}, DOI={10.1021/es900535s}, abstractNote={This study presents a methodology for estimating high-resolution, regional on-road vehicle emissions and the associated reductions in air pollutant emissions from vehicles that utilize alternative fuels or propulsion technologies. The fuels considered are gasoline, diesel, ethanol, biodiesel, compressed natural gas, hydrogen, and electricity. The technologies considered are internal combustion or compression engines, hybrids, fuel cell, and electric. Road link-based emission models are developed using modal fuel use and emission rates applied to facility- and speed-specific driving cycles. For an urban case study, passenger cars were found to be the largest sources of HC, CO, and CO(2) emissions, whereas trucks contributed the largest share of NO(x) emissions. When alternative fuel and propulsion technologies were introduced in the fleet at a modest market penetration level of 27%, their emission reductions were found to be 3-14%. Emissions for all pollutants generally decreased with an increase in the market share of alternative vehicle technologies. Turnover of the light duty fleet to newer Tier 2 vehicles reduced emissions of HC, CO, and NO(x) substantially. However, modest improvements in fuel economy may be offset by VMT growth and reductions in overall average speed.}, number={21}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Frey, H. Christopher and Zhai, Haibo and Rouphail, Nagui M.}, year={2009}, month={Nov}, pages={8449–8455} }
 @article{schroeder_rouphail_hughes_2009, title={Working concept of accessibility performance measures for usability of crosswalks by pedestrians with vision impairments}, number={2140}, journal={Transportation Research Record}, author={Schroeder, B. J. and Rouphail, N. M. and Hughes, R. G.}, year={2009}, pages={103–110} }
 @article{zhai_frey_rouphail_2008, title={A Vehicle-Specific Power Approach to Speed- and Facility-Specific Emissions Estimates for Diesel Transit Buses}, volume={42}, ISSN={["1520-5851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-55349085068&partnerID=MN8TOARS}, DOI={10.1021/es800208d}, abstractNote={Emissions during a trip often depend on transient vehicle dynamics that influence the instantaneous engine load. Vehicle specific power (VSP) is a proxy variable for engine load that has been shown to be highly correlated with emissions. This study estimates roadway link average emission rates for diesel-fueled transit buses based on link mean speeds, using newly defined VSP modes from data gathered by a portable emissions monitoring system. Speed profiles were categorized by facility type and mean travel speed, and stratified into discrete VSP modes. VSP modal average emission rates and the time spent in the corresponding VSP modes were then used to make aggregate estimates of total and average emission rates for a road link. The average emission rates were sensitive to link mean speed, but not to facility type. A recommendation is made regarding the implementation of link average emission rates in conjunction with transportation models for the purpose of estimating regional emissions for diesel transit buses.}, number={21}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Zhai, Haibo and Frey, H. Christopher and Rouphail, Nagui M.}, year={2008}, month={Nov}, pages={7985–7991} }
 @article{flannery_rouphail_reinke_2008, title={Analysis and modeling of automobile users' perceptions of quality of service on urban streets}, number={2071}, journal={Transportation Research Record}, author={Flannery, A. and Rouphail, N. and Reinke, D.}, year={2008}, pages={26–34} }
 @article{frey_zhang_rouphail_2008, title={Fuel use and emissions comparisons for alternative routes, time of day, road grade, and vehicles based on in-use measurements}, volume={42}, ISSN={["1520-5851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-41649109289&partnerID=MN8TOARS}, DOI={10.1021/es702493v}, abstractNote={The objective here is to quantify the variability in emissions of selected light duty gasoline vehicles by routes, time of day, road grade, and vehicle with a focus on the impact of routes and road grade. Field experiments using a portable emission measurement system were conducted under real-world driving cycles. The study area included two origin/destination pairs, each with three alternative routes. Total emissions varied from trip to trip and from route to route due to variations in average speed and travel time. On an average trip basis, the total NO emissions differed by 24% when comparing alternative routes and by 19% when comparing congested travel time with less congested traffic time. Positive road grades were associated with an approximately 20% increase in localized emissions rates, while negative road grades were associated with a similar relative decrease. The average vehicle-specific power based NO modal emission rates differed by more than 2 orders of magnitude when comparing different vehicles. The results demonstrate that alternative routing can significantly impact trip emissions. Furthermore, road grade should be taken into account for localized emissions estimation. Vehicle-specific models are needed to capture episodic effects of emissions for near-road short-term human exposure assessment.}, number={7}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Frey, H. Christopher and Zhang, Kaishan and Rouphail, Nagui M.}, year={2008}, month={Apr}, pages={2483–2489} }
 @inproceedings{zhai_frey_rouphail_gonçalves_farias_2008, title={Impact of Alternative Vehicle Technologies on Measured Vehicle Emissions}, volume={320}, ISBN={9780784409602}, url={http://dx.doi.org/10.1061/40960(320)38}, DOI={10.1061/40960(320)38}, abstractNote={Emerging vehicle technologies such as hybrids, flex-fuel, electric, and fuel cells are projected to exceed 25% of total light-duty vehicle sales by 2030. Because of their higher energy efficiency, hybrid electric vehicles (HEVs) produce lower emissions of greenhouse gases such as CO 2 than comparable gasoline vehicles. Measurements of selected advanced gasoline and diesel direct injection vehicles and gasoline-electric hybrid vehicles indicate that the HEV had the lowest emissions and highest fuel economy. One study concluded that replacing all conventional vehicles with HEV's could cut total CO and NO x emissions in half. Flex-fuel vehicles that can use either gasoline or ethanol 85 (E85), a blend of 85% ethanol and 15% gasoline by volume have sensors that can analyze the fuel-air mixture and adjust the fuel injection and timing. Since ethanol is an oxygenated fuel, the use of ethanol may reduce emissions of products of incomplete combustion including CO and HC. However, the oxygenate may tend to increase NO x emissions because of lean combustion. The use of blends with a high percentage of ethanol in the mix was found to produce increased emissions of NO x and aldehydes as the ethanol content increased. However, measurements of flex-fuel Chevrolet Lumina vehicles indicated that the use of E85 may decrease vehicle CO, HC and NO x emissions, but increase aldehydes emissions when compared to gasoline vehicles showed that NO x emissions increased with increasing ethanol content for some fuels, but were unaffected by ethanol content for other fuels, depending on fuel volatility. Hochhauser found that use of ethanol fuel may increase vehicle permeation emissions of VOC. Therefore, flex-fuel vehicles do not assure lower emissions for at least some pollutants compared to dedicated gasoline vehicles. The objective of this study is to develop an advanced modeling system to quantify influences of land use and vehicle technologies on on-road vehicle emissions such as CO 2 , CO, and NO x . The main focus here is to demonstrate a methodology for assessing how differences in driving cycles affect link-based average emission rates for selected vehicle technologies. The methodology requires second-by-second data, with a preference for real-world in-use data where possible. The methodology is illustrated here based on data from one flex-fuel vehicle that was measured during actual driving using a portable emission measurement system (PEMS) on both gasoline and E85 and for one HEV that was tested on a chassis dynamometer. Testing for the flex-fueled vehicle was conducted by Instituto Superior Tecnico (IST) in Lisbon, Portugal. The flex-fuel vehicle is a European 2006 flex-fuel Ford Focus wagon with a 1.8 liter engine (92 kW/6000rpm, 165 Nm/4000rpm). By comparison, the U.S. version of the Focus has a 2.0 liter engine (97 kW/6000rpm, 175 Nm/4000rpm). The HEV is a 2001 Toyota Prius with a 1.5 liter gasoline engine.}, booktitle={Transportation Land Use, Planning, and Air Quality}, publisher={American Society of Civil Engineers}, author={Zhai, H. and Frey, H. C. and Rouphail, N. M. and Gonçalves, G. A. and Farias, T. L.}, year={2008}, month={May} }
 @article{frey_rouphail_zhai_2008, title={Link-based emission factors for heavy-duty diesel trucks based an real-world data}, number={2058}, journal={Transportation Research Record}, author={Frey, H. C. and Rouphail, N. M. and Zhai, H. B.}, year={2008}, pages={23–32} }
 @article{dowling_flannery_landis_petritsch_rouphail_ryus_2008, title={Multimodal level of service for urban streets}, number={2071}, journal={Transportation Research Record}, author={Dowling, R. and Flannery, A. and Landis, B. and Petritsch, T. and Rouphail, N. and Ryus, P.}, year={2008}, pages={1–7} }
 @article{schroeder_rouphail_hughes_2008, title={Toward roundabout accessibility - Exploring the operational impact of pedestrian signalization options at modern roundabouts}, volume={134}, DOI={10.1061/(ASCE)0733-947X(2008)134:6(262)}, abstractNote={This paper explores the use of pedestrian signalization options for crosswalks at one- and two-lane roundabouts to enable these facilities to be accessible to pedestrians with vision impairments. Motivated by uncertainties about the safety of roundabouts for blind pedestrians, audible pedestrian signals hold promise for safely regulating the interaction of vehicles and pedestrians at these facilities. However, the use of pedestrian signals at roundabouts is controversial because of the potential for queue spillback into the circulating lane and delays to vehicular traffic. The objective of this work is to quantify pedestrian-induced delays and queuing impacts of a pedestrian signal placed at the busiest approach of a modern roundabout. The analysis is performed using a calibrated microsimulation model and includes assessment of innovative solutions for crossing geometry and phasing scheme at one-lane and two-lane roundabouts. The results suggest that the impact of pedestrian signals at roundabouts is greatest as vehicle volumes approach capacity, but that vehicle delay and queuing can be mitigated through innovative signal configurations. The findings are important in light of recent discourse concerning the accessibility of roundabouts to pedestrians with vision impairments that may ultimately move towards a requirement for signalization for certain facility types.}, number={6}, journal={Journal of Transportation Engineering}, author={Schroeder, B. J. and Rouphail, N. M. and Hughes, R. G.}, year={2008}, pages={262–271} }
 @article{khattak_pan_williams_rouphail_fan_2008, title={Traveler information delivery mechanisms impact on consumer behavior}, number={2069}, journal={Transportation Research Record}, author={Khattak, A. J. and Pan, X. H. and Williams, B. and Rouphail, N. and Fan, Y. L.}, year={2008}, pages={77–84} }
 @article{frey_rouphail_zhai_farias_goncalves_2007, title={Comparing real-world fuel consumption for diesel- and hydrogen-fueled transit buses and implication for emissions}, volume={12}, ISSN={["1361-9209"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-34247868934&partnerID=MN8TOARS}, DOI={10.1016/j.trd.2007.03.003}, abstractNote={This paper explores the influence of key factors such as speed, acceleration, and road grade on fuel consumption for diesel and hydrogen fuel cell buses under real-world operating conditions. A Vehicle Specific Power-based approach is used for modeling fuel consumption for both types of buses. To evaluate the robustness of the modeling approach, Vehicle Specific Power-based modal average fuel consumption rates are compared for diesel buses in the US and Portugal, and for the Portuguese diesel and hydrogen fuel cell buses that operate on the same route. For diesel buses there is similar intra-vehicle variability in fuel consumption using Vehicle Specific Power modes. For the fuel cell bus, the hydrogen fuel consumption rate was found to be less sensitive to Vehicle Specific Power variations and had smaller variability compared to diesel buses. Relative errors between trip fuel consumption estimates and actual fuel use, based upon predictions for a portion of real-world activity data that were not used to calibrate the models, were generally under 10% for all observations. The Vehicle Specific Power-based modeling approach is recommended for further applications as additional data become available. Emission changes based upon substituting hydrogen versus diesel buses are evaluated.}, number={4}, journal={TRANSPORTATION RESEARCH PART D-TRANSPORT AND ENVIRONMENT}, author={Frey, H. Christopher and Rouphail, Nagui M. and Zhai, Haibo and Farias, Tiago L. and Goncalves, Goncalo A.}, year={2007}, month={Jun}, pages={281–291} }
 @article{williams_tagliaferri_meinhold_hummer_rouphail_2007, title={Simulation and analysis of freeway lane reversal for coastal hurricane evacuation}, volume={133}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33847207471&partnerID=MN8TOARS}, DOI={10.1061/(ASCE)0733-9488(2007)133:1(61)}, abstractNote={Following the unprecedented multistate evacuation for Hurricane Floyd in 1999, the North Carolina Department of Transportation and the Department of Crime Control and Public Safety jointly developed a lane reversal plan for Interstate 40 to facilitate evacuation of residents and tourists in southeastern North Carolina. Prior to the 2003 hurricane season, the NCDOT sponsored a two-year research to address areas of operational concern. The first year research findings resulted in modifications to the original lane reversal plan. The second year's findings showed the modified reversal plan to be effective in expediting evacuation from the coastal threat zone. However, modeling of the entire lane reversal plan revealed a potentially extensive queue formation at the contraflow termination point. This paper presents an overview of the project along with the principal research findings and resulting plan modifications. In addition, this paper highlights conclusions and recommendations applicable to the general emergency evacuation problem.}, number={1}, journal={Journal of Urban Planning and Development}, author={Williams, Billy and Tagliaferri, A.P. and Meinhold, S.S. and Hummer, J.E. and Rouphail, N.M.}, year={2007}, pages={61–72} }
 @article{coelho_farias_rouphail_2006, title={Effect of roundabout operations on pollutant emissions}, volume={11}, ISSN={["1361-9209"]}, DOI={10.1016/j.trd.2006.06.005}, abstractNote={This research quantifies the traffic and emission impacts of single lane roundabouts in urban corridors, based on experimental measurements of traffic and using the “Vehicle Specific Power” emission estimation methodology. Experimental data were gathered from single lane roundabouts located in Lisbon (Portugal) and Raleigh (US). Using congestion-specific vehicle speed profiles on the roundabout approaches, the emissions calculation methodology is able to quantify the relationships between vehicle dynamics and emissions. The main contributions are: the characterization of a limited set of synthetic speed profiles that occur at a roundabout approach, the frequency distribution of these profiles based on congestion levels, and the correlation between queue length and the number of stop and go cycles. Two different types of stop and go driving cycles for vehicles joining the queue at a roundabout were identified: short and long.}, number={5}, journal={TRANSPORTATION RESEARCH PART D-TRANSPORT AND ENVIRONMENT}, author={Coelho, Margarida C. and Farias, Tiago L. and Rouphail, Nagul M.}, year={2006}, month={Sep}, pages={333–343} }
 @article{silva_farias_frey_rouphail_2006, title={Evaluation of numerical models for simulation of real-world hot-stabilized fuel consumption and emissions of gasoline light-duty vehicles}, volume={11}, ISSN={["1361-9209"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33748436974&partnerID=MN8TOARS}, DOI={10.1016/j.trd.2006.07.004}, abstractNote={The use of numerical models for estimating fuel consumption and emission of HC, CO, NOx and CO2 of gasoline vehicles, under urban driving conditions, is examined. Three models were selected for evaluation: EcoGest, CMEM and ADVISOR. The models were used to simulate a sample of 14 urban trips for two 1999 Ford Taurus vehicles. Trip statistics were monitored on-board of the passenger vehicles across a variety of traffic conditions, using a portable emissions measurement device (PEMS). A key conclusion is that the tested models can be used with relatively high confidence to predict fuel consumption and CO2 emissions. However, results must be viewed with greater caution when it comes to predictions for other pollutants.}, number={5}, journal={TRANSPORTATION RESEARCH PART D-TRANSPORT AND ENVIRONMENT}, author={Silva, C. M. and Farias, T. L. and Frey, H. Christopher and Rouphail, Nagui M.}, year={2006}, month={Sep}, pages={377–385} }
 @article{coelho_farias_rouphail_2005, title={A methodology for modelling and measuring traffic and emission performance of speed control traffic signals}, volume={39}, ISSN={["1873-2844"]}, DOI={10.1016/j.atmosenv.2004.03.082}, abstractNote={In an attempt to control speeds and reduce crashes, traffic signals are being installed at several locations on highways to serve as speed reduction devices. One concern about this type of signals is that while they may be effective in reducing high speed crashes, they not only stop traffic that is exceeding the speed limit, but other traffic on the approach that is not. As a result, vehicle emissions are likely to increase, because of the existence of excessive delays, queue formation and speed change cycles for approaching traffic. An approach, based on experimental measurements and on modelling traffic and emission performance of speed control traffic signals, is presented here in order to explain the interaction between the signal control variables (for example minimum signal settings, speed threshold setting and minimum green call scenarios) and environmental and traffic performance variables, in particular, carbon monoxide, nitric oxide and hydrocarbons emissions and delay. The experimental data for validation were gathered on Highway N6, connecting the cities of Lisbon and Cascais, in Portugal. The main conclusions of the present research are that, for traffic flow values corresponding to 50% of the road capacity estimate for a traffic signal approach, 85% of the speed violators are effectively stopped, while the fraction of vehicles unfairly stopped reaches 30%. Concerning emissions the presence of signals leads to an increase in CO emissions of about 15%, while NO and HC emissions increase by 10% and 40%, respectively. It was also concluded that the control of speed violators increases with traffic flow. As a trade-off, overall traffic delay will also increase as well as the number of vehicles that are unfairly stopped.}, number={13}, journal={ATMOSPHERIC ENVIRONMENT}, author={Coelho, MC and Farias, TL and Rouphail, NM}, year={2005}, month={Apr}, pages={2367–2376} }
 @inbook{paulo_lin_rouphail_sacks_2005, title={Calibrating and validating deterministic traffic models: application to the HCM control delay at signalized intersections}, ISBN={0309093856}, number={1912}, booktitle={Geometric design and the effects on traffic operations, 2005}, publisher={Washington, DC: Transportation Research Board}, author={Paulo, R. and Lin, J. and Rouphail, N. and Sacks, J.}, year={2005}, pages={95–105} }
 @article{rouphail_hughes_chae_2005, title={Exploratory simulation of pedestrian crossings at roundabouts}, volume={131}, DOI={10.1061/(ASCE)0733-947X(2005)131:3(211)}, abstractNote={There is presently much debate over the issue of pedestrian access to highway facilities, particularly for those who are blind or function with low vision. This issue is now the focus of current United States Access Board draft recommendations, which propose that signalization is necessary to ensure safe access for blind pedestrians at roundabouts. The objective of this research was to capture the gap acceptance behavior for both sighted and blind pedestrians near roundabouts (revealed from a parallel research effort) and integrate that behavior into a microscopic simulation model of pedestrian and vehicular traffic operations at a roundabout. This process enables the quantification of the mutual impact of pedestrian crossing behavior on vehicle operation, and of motorized traffic impact on pedestrian access (or delay). In addition, it allows the conduct of experiments targeted at evaluating various pedestrian treatments at or in the vicinity of the roundabout. The simulation results indicated that pedestrian delay increases in a nonlinear fashion as vehicle volume increased. In addition, while there was a small difference in sighted pedestrian delays at the entry and exit legs, that difference was more pronounced for blind pedestrians who experienced higher delays on the exit side. Finally, an analysis of pedestrian crossing treatments indicated that placing a pedestrian-actuated, signalized crossing upstream/ downstream of the roundabout results in delays to blind pedestrians that are comparable to those experienced by sighted pedestrians that cross at the unsignalized splitter island. The location of the crossing was assessed on the basis of queue spillback probabilities onto the roundabout exit leg.}, number={3}, journal={Journal of Transportation Engineering}, author={Rouphail, N. and Hughes, R. and Chae, K.}, year={2005}, pages={211–218} }
 @article{coelho_farias_rouphail_2005, title={Impact of speed control traffic signals on pollutant emissions}, volume={10}, ISSN={["1361-9209"]}, DOI={10.1016/j.trd.2005.04.005}, abstractNote={The paper uses experimental measurements to explain the interaction between the signal control settings and emissions and traffic variables. The data for validation were gathered on Highway N6, connecting the cities of Lisbon and Cascais, in Portugal. Emissions are computed based on a modal approach. Trade-offs between level of enforcement against added emissions are explored. One of the main conclusions of the research is that signal control schemes that result in stopping a larger fraction of speed violators also yield higher emissions. On the other hand, if the speed control traffic signals modify drivers’ behaviour by inducing speed reduction, they will also result in a decrease in relative pollutant emissions.}, number={4}, journal={TRANSPORTATION RESEARCH PART D-TRANSPORT AND ENVIRONMENT}, author={Coelho, MC and Farias, TL and Rouphail, NM}, year={2005}, month={Jul}, pages={323–340} }
 @inbook{lee_rouphail_hummer_2005, title={Lane utilization prediction models for lane-drop intersections}, ISBN={0309093856}, number={1912}, booktitle={Geometric design and the effects on traffic operations, 2005}, publisher={Washington, DC: Transportation Research Board}, author={Lee, J. and Rouphail, N. and Hummer, J.}, year={2005}, pages={47–56} }
 @article{do_hummer_toole_rouphail_2005, title={Making Trails}, volume={69}, number={1}, journal={Public Roads}, author={Do, A. and Hummer, J. and Toole, J. and Rouphail, N.}, year={2005}, pages={12–17} }
 @article{coelho_farias_rouphail_2005, title={Measuring and modeling emission effects for toll facilities}, ISBN={["0-309-09416-X"]}, ISSN={["0361-1981"]}, DOI={10.3141/1941-17}, abstractNote={At conventional pay tolls, vehicles joining a queue must come to a stop and undergo several stop-and-go cycles until payment is completed. As a result, emissions increase because of excessive delays, queuing, and speed change cycles for approaching traffic. The main objective of this research is to quantify traffic and emission impacts of toll facilities in urban corridors. As a result of experimental measurements of traffic and emissions, the impact of traffic and emission performance of conventional and electronic toll facilities is presented. The approach attempts to explain the interaction between toll system operational variables (traffic demand, service time, and service type) and system performance variables (stops, queue length, and emissions). The experimental data for validating the numerical traffic model were gathered on pay tolls located in three main corridors that access the city of Lisbon, Portugal. The emissions model is based on real-world onboard measurements of vehicle emissions. With the appropriate speed profiles of vehicles in pay tolls, onboard emission measurements were carried out to quantify the relationships between vehicle dynamics and emissions. The main conclusion of this work is that there are two different types of stop-and-go driving cycles for vehicles joining the queue at a conventional toll booth: short and long. The length of each cycle depends on the expected queue length at the toll booth and the frequency of each cycle directly affects the level of vehicle emissions. The greatest percentage of emissions for a vehicle that stops at a pay toll is due to its final acceleration back to cruise speed after leaving the pay toll.}, number={1941}, journal={ENERGY AND ENVIRONMENTAL CONCERNS 2005}, author={Coelho, MC and Farias, TL and Rouphail, NM}, year={2005}, pages={136–144} }
 @inbook{coelho_farias_rouphail_2005, title={Measuring and modeling emissions effects for toll facilities}, booktitle={Transportation Research Record}, publisher={Washington, DC: Transportation Research Board}, author={Coelho, M. and Farias, T. and Rouphail, N.}, year={2005} }
 @inbook{hummer_rouphail_hughes_fain_toole_patten_schneider_monahan_do_2005, title={User perceptions of the quality of service on shared paths}, ISBN={0309094135}, number={1939}, booktitle={Bicycles and pedestrians:  Developing countries, 2005}, publisher={Washington, D.C.: Transportation Research Board}, author={Hummer, J. E. and Rouphail, N. and Hughes, R. G. and Fain, S. J. and Toole, J. L. and Patten, R. S. and Schneider, R. J. and Monahan, J. F. and Do, A.}, year={2005}, pages={28–36} }
 @inbook{bayarri_berger_molina_rouphail_sacks_2004, title={Assessing uncertainties in traffic simulation: A key component in model calibration and validation}, ISBN={0309094704}, number={1876}, booktitle={Calibration and validation of simulation models 2004}, publisher={Washington, DC: Transportation Research Board}, author={Bayarri, M. J. and Berger, J. O. and Molina, G. and Rouphail, N. M. and Sacks, J.}, year={2004}, pages={32–40} }
 @inbook{torres_nelson_rouphail_raj_2004, title={Estimating link delays for arterial streets}, ISBN={1843763060}, booktitle={Urban and regional transportation modeling, essays in honor of David Boyce}, publisher={Northhampton, MA: Edward Elgar}, author={Torres, E. and Nelson, P. and Rouphail, N. and Raj, J.}, year={2004} }
 @inbook{khattak_rouphail_monast_havel_2004, title={Method for priority-ranking and expanding freeway service patrols}, ISBN={0309094615}, number={1867}, booktitle={Freeway operations and traffic signal systems, 2004}, publisher={Washington, DC: Transportation Research Board, National Academy of Sciences}, author={Khattak, A. and Rouphail, N. and Monast, K. and Havel, J.}, year={2004}, pages={1–10} }
 @inbook{khattak_rouphail_monast_havel_2004, title={Methodology for prioritizing and expanding freeway service patrols}, ISBN={0309094704}, number={1876}, booktitle={Calibration and validation of simulation models 2004}, publisher={Washington, DC: Transportation Research Board}, author={Khattak, A. and Rouphail, N. and Monast, K. and Havel, J.}, year={2004}, pages={1–10} }
 @article{unal_frey_rouphail_2004, title={Quantification of highway vehicle emissions hot spots based upon on-board measurements}, volume={54}, ISSN={["2162-2906"]}, DOI={10.1080/10473289.2004.10470888}, abstractNote={The purpose of this study is to demonstrate a methodology for quantification of high emissions hot spots along roadways based upon real-world, on-road vehicle emissions measurements. An emissions hot spot is defined as a fixed location along a corridor in which the peak emissions are statistically significantly greater by more than a factor of 2 than the average emissions for free-flow or near free-flow conditions on the corridor. A portable instrument was used to measure on-road tailpipe emissions of carbon monoxide, nitric oxide, hydrocarbons, and carbon dioxide on a second-by-second basis during actual driving. Measurements were made for seven vehicles deployed on two primary arterial corridors. The ratio of average emissions at hot spots to the average emissions observed during a trip was as high as 25 for carbon monoxide, 5 for nitric oxide, and 3 for hydrocarbons. The relationships between hot spots and explanatory variables were investigated using graphical and statistical methods. Average speed, average acceleration, standard deviation of speed, percent of time spent in cruise mode, minimum speed, maximum acceleration, and maximum power have statistically significant associations with vehicle emissions and influence emissions hot spots. For example, stop-and-go traffic conditions that result in sudden changes in speed, and traffic patterns with high accelerations, are shown to generate hot spots. The implications of this work for future model development and applications to environmental management are discussed.}, number={2}, journal={JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION}, author={Unal, A and Frey, HC and Rouphail, NM}, year={2004}, month={Feb}, pages={130–140} }
 @inbook{wan_rouphail_2004, title={Using arena for simulation of pedestrian crossing in roundabout areas}, ISBN={0309094720}, number={1878}, booktitle={Pedestrians and bicycles: Developing countries}, publisher={Washington, DC: Transportation Research Board}, author={Wan, B. H. and Rouphail, N. M.}, year={2004}, pages={58–65} }
 @article{a  statistically-based validation of computer simulation models in traffic operations and management_2003, volume={5}, number={1}, journal={Journal of Transportation and Statistics}, year={2003}, pages={1–15} }
 @inbook{hagring_rouphail_sorensen_2003, title={Comparison of capacity models for two-lane roundabouts}, ISBN={0309085888}, number={1852}, booktitle={Traffic flow theory and highway capacity, 2003}, publisher={Washington, DC: Transportation Research Board}, author={Hagring, O. and Rouphail, N. M. and Sorensen, H. A.}, year={2003}, pages={114–123} }
 @inbook{unal_rouphail_frey_2003, title={Effect of arterial signalization and level of service on measured vehicle emissions}, ISBN={0309085756}, number={1842}, booktitle={Energy, air quality, and fuels 2003}, publisher={Washington, DC: Transportation Research Board}, author={Unal, A. and Rouphail, N. M. and Frey, H. C.}, year={2003}, pages={47–56} }
 @inbook{colyar_rouphail_2003, title={Measured distributions of control delay on signalized arterials}, ISBN={0309085888}, number={1852}, booktitle={Traffic flow theory and highway capacity, 2003}, publisher={Washington, DC: Transportation Research Board}, author={Colyar, J. D. and Rouphail, N. M.}, year={2003}, pages={1–9} }
 @article{frey_unal_rouphail_colyar_2003, title={On-road measurement of vehicle tailpipe emissions using a portable instrument}, volume={53}, ISSN={["2162-2906"]}, DOI={10.1080/10473289.2003.10466245}, abstractNote={Abstract A study design procedure was developed and demonstrated for the deployment of portable onboard tailpipe emissions measurement systems for selected highway vehicles fueled by gasoline and E85 (a blend of 85% ethanol and 15% gasoline). Data collection, screening, processing, and analysis protocols were developed to assure data quality and to provide insights regarding quantification of real-world intravehicle variability in hot-stabilized emissions. Onboard systems provide representative real-world emissions measurements; however, onboard field studies are challenged by the observable but uncontrollable nature of traffic flow and ambient conditions. By characterizing intravehicle variability based on repeated data collection runs with the same driver/vehicle/route combinations, this study establishes the ability to develop stable modal emissions rates for idle, acceleration, cruise, and deceleration even in the face of uncontrollable external factors. For example, a consistent finding is that average emissions during acceleration are typically 5 times greater than during idle for hydrocarbons and carbon dioxide and 10 times greater for nitric oxide and carbon monoxide. A statistical method for comparing on-road emissions of different drivers is presented. Onboard data demonstrate the importance of accounting for the episodic nature of real-world emissions to help develop appropriate traffic and air quality management strategies.}, number={8}, journal={JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION}, author={Frey, HC and Unal, A and Rouphail, NM and Colyar, JD}, year={2003}, month={Aug}, pages={992–1002} }
 @article{nevers_rouphail_2002, title={Field evaluation of lane selection strategies at signalized intersections}, volume={128}, DOI={10.1061/(ASCE)0733-947X}, number={3}, journal={Journal of Transportation Engineering}, author={Nevers, B. and Rouphail, N.}, year={2002}, pages={224–231} }
 @inbook{rouphail_nevers_2001, title={A saturation flow rate using traffic subgroups}, ISBN={0309072344}, number={1776}, booktitle={Traffic flow theory and highway capacity 2001}, publisher={Washington, D.C.: National Academy Press}, author={Rouphail, N. M. and Nevers, B. L.}, year={2001}, pages={114–122} }
 @inbook{rhoulac_rouphail_tsai_2001, title={Application of GPS to pupil transportation operations}, ISBN={0309072301}, number={1768}, booktitle={Transportation data and information technology
Council, 2001.}, publisher={Washington, DC: Transportation Research Board, National Research 
Council, 2001.}, author={Rhoulac, T. and Rouphail, N. and Tsai, J.}, year={2001}, pages={242–249} }
 @inbook{park_rouphail_sacks_2001, title={Assessment of stochastic signal optimization method using microsimulation}, ISBN={0309072077}, number={1748}, booktitle={Advanced traffic management systems and vehicle-highway automation 2001: Highway operations, capacity, and traffic 
control. Washington, D.C.: National Academy Press, 2001.}, publisher={Washington, DC: National Academy Press}, author={Park, B. and Rouphail, N. M. and Sacks, J.}, year={2001}, pages={40–45} }
 @article{park_rouphail_hochanadel_sacks_2001, title={Evaluating reliability of TRANSYT-7F optimization schemes}, volume={127}, DOI={10.1061/(ASCE)0733-947X(2001)127:4(319)}, abstractNote={This paper investigates the reliability of TRANSYT-7F optimal solutions from two perspectives: (1) the effect of the selected optimization criterion on the values of various system performance measures; and (2) the extent to which TRANSYT-7F signal plans remain optimal when evaluated in a microscopic and stochastic traffic environment. The well-established CORSIM model was used for the latter test. A customized code has been developed that can automatically generate statistical distributions of selected performance measures in CORSIM based on various TRANSYT-7F optimization runs. The method has been applied to a calibrated test network in Chicago consisting of 9 signalized intersections with 50 nodes and 74 links. It was found that while good correlation existed between the corresponding performance measures in TRANSYT-7F and CORSIM under light traffic, their correlation diminished under congested flow. In particular, the best signal strategy identified in TRANSYT-7F was not the best in the CORSIM environment. The discrepancies are undoubtedly due to the basic difference between the two models: TRANSYT-7F is deterministic, CORSIM is stochastic.}, number={4}, journal={Journal of Transportation Engineering}, author={Park, B. and Rouphail, N. and Hochanadel, J. and Sacks, J.}, year={2001}, pages={319–326} }
 @inbook{may_rouphail_bloomberg_hall_urbanik_2001, title={Freeway systems research beyond Highway Capacity Manual 2000}, ISBN={0309072344}, number={1776}, booktitle={Traffic flow theory and highway capacity 2001}, publisher={Washington, DC: National Academy Press}, author={May, A. D. and Rouphail, N. and Bloomberg, L. and Hall, F. and Urbanik, T.}, year={2001}, pages={1–9} }
 @article{eldessouki_fathi_rouphail_2001, title={Meta-optimization using cellular automata with application to the combined trip distribution and assignment system optimal problem}, volume={16}, ISSN={["1093-9687"]}, DOI={10.1111/0885-9507.00241}, abstractNote={In this paper, meta‐optimization and cellular automata have been introduced as a modeling environment for solving large‐scale and complex transportation problems. A constrained system optimum combined trip distribution and assignment problem was selected to demonstrate the applicability of the cellular automata approach over classical mixed integer formulation. A mathematical formulation for the selected problem has been developed and a methodology for applying cellular automata has been presented. A numerical example network was used to illustrate the potential for using cellular automata as a modeling environment for solving optimization problems.}, number={6}, journal={COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING}, author={ElDessouki, WM and Fathi, Y and Rouphail, N}, year={2001}, month={Nov}, pages={384–398} }
 @inbook{rouphail_nevers_2001, title={Saturation flow estimation by traffic subgroups}, ISBN={0309072344}, number={1776}, booktitle={Traffic flow theory and highway capacity 2001}, publisher={Washington, DC: National Academy Press}, author={Rouphail, N. M. and Nevers, B. L.}, year={2001}, pages={114–122} }
 @inbook{rhoulac_rouphail_tsai_2001, title={Using global positioning system to improve school bus routing and scheduling}, ISBN={0309072301}, number={1768}, booktitle={Transportation data and information technology}, publisher={Washington, DC: Transportation Research Board}, author={Rhoulac, T. D. and Rouphail, N. and Tsai, J. C.}, year={2001}, pages={242–249} }
 @inbook{eads_rouphail_may_hall_2000, title={Freeway facility methodology in Highway Capacity Manual 2000}, number={1710}, booktitle={Traffic flow theory and highway capacity, 2000}, publisher={Washington, DC: National Academy Press}, author={Eads, B. S. and Rouphail, N. M. and May, A. D. and Hall, F.}, year={2000}, pages={171–180} }
 @article{park_rouphail_hummer_2000, title={Probabilistic approach to implementing traffic signal warrants}, journal={Journal of Transportation Engineering}, author={Park, B. and Rouphail, N. and Hummer, J.}, year={2000}, pages={332–343} }
 @inbook{hall_bloomberg_rouphail_eads_may_2000, title={Validation results for four models of oversaturated freeway facilities}, number={1710}, booktitle={Traffic flow theory and highway capacity, 2000}, publisher={Washington, DC: National Academy Press}, author={Hall, F. L. and Bloomberg, L. and Rouphail, N. M. and Eads, B. and May, A. D.}, year={2000}, pages={161–170} }
 @inbook{milazzo_rouphail_hummer_allen_1999, title={Quality of service for interrupted flow facilities in highway capacity manual 2000}, ISBN={0309071046}, number={1678}, booktitle={Highway capacity, quality of service, and traffic flow and characteristics}, publisher={Washington, D.C.: National Academy Press}, author={Milazzo, J. S. and Rouphail, N. and Hummer, J. and Allen, P.}, year={1999}, pages={25–31} }
 @inproceedings{bloomberg_clark_cohen_eads_hall_may_rathi_rouphail_urbanik_1998, title={Capacity and level of service analysis of freeway systems}, number={1998 June}, booktitle={Proceedings, Third International Symposium on Highway Capacity, Copenhagen, Denmark, June 22-27, 1998}, author={Bloomberg, L. and Clark, J. and Cohen, S. and Eads, B. and Hall, F. and May, A. and Rathi, A. and Rouphail, N. and Urbanik, T.}, year={1998} }
 @inproceedings{rouphail_fambro_1998, title={Delay and queue length models for congested arterials}, number={1998 June}, booktitle={Proceedings, Third International Symposium on Highway Capacity, Copenhagen, Denmark, June 22-27, 1998}, author={Rouphail, N. and Fambro, D.}, year={1998} }
 @inbook{allen_hummer_rouphail_milazzo_1998, title={Effect of bicycles on capacity of signalized intersections}, ISBN={0309065186}, number={1646}, booktitle={Highway capacity issues, 1998}, publisher={Washington, DC: Transportation Research Board}, author={Allen, D. P. and Hummer, J. E. and Rouphail, N. M. and Milazzo, J. S.}, year={1998}, pages={87–95} }
 @inbook{milazzo_rouphail_hummer_allen_1998, title={Effect of pedestrians on capacity of signalized intersections}, ISBN={0309065186}, number={1646}, booktitle={Highway capacity issues, 1998}, publisher={Washington, DC: Transportation Research Board}, author={Milazzo, J. S. and Rouphail, N. M. and Hummer, J. E. and Allen, D. P.}, year={1998}, pages={37–46} }
 @inbook{rouphail_al._1998, title={Literature synthesis: Pedestrians: Final report}, booktitle={Highway capacity manual; Chapter 13: Pedestrians, final report submitted to the Highway Safety Research Center}, publisher={Washington, DC: National Academy Press}, author={Rouphail, N. M. and al.}, year={1998} }
 @inbook{eldessouki_rouphail_beja_ranjithan_1998, title={Multiperiod highway improvement and construction scheduling: Model development and application}, ISBN={0309064627}, number={1617}, booktitle={Land use and transportation planning and programming applications}, publisher={Washington, DC: Transportation Research Board}, author={Eldessouki, W. and Rouphail, N. and Beja, M. and Ranjithan, S. R.}, year={1998}, pages={96–104} }
 @inproceedings{rouphail_hummer_goldblatt_1998, title={Pedestrian and bicycle impacts on signalized intersection operations: the U.S. experience}, volume={2}, number={1998}, booktitle={Proceedings of the Third International Symposium on Highway Capacity, Copenhagen, Denmark, June 22-27, 1998}, author={Rouphail, N. M. and Hummer, J. E. and Goldblatt, R.}, year={1998}, pages={852–872} }
 @inbook{rouphail_al._1998, title={Recommended Procedures: Bicycles: Final report}, booktitle={Highway capacity manual; Chapter 14: Bicycles, Final report submitted to the Highway Safety Research Center}, publisher={Washington, DC: National Academy Press}, author={Rouphail, N. M. and al.}, year={1998} }
 @inbook{rouphail_al._1998, title={Recommended Procedures: Pedestrians: Final report}, booktitle={Highway capacity manual; Chapter 13: Pedestrians, final report submitted to the Highway Safety Research Center}, publisher={Washington, DC: National Academy Press}, author={Rouphail, N. M. and al.}, year={1998} }
 @inbook{rouphail_al._1998, title={Research report and recommended procedures: Signalized intersections}, booktitle={Highway capacity manual; Chapter 9: Signalized Intersections, Final report submitted to the Highway Safety Research Center}, publisher={Washington, DC: National Academy Press}, author={Rouphail, N. M. and al.}, year={1998} }
 @inbook{allen_hummer_rouphail_milazzo_1998, title={The Effects of bicycles on the capacity of signalized intersections}, ISBN={0309065186}, number={1646}, booktitle={Highway capacity issues, 1998}, publisher={Washington, DC: National Academy Press}, author={Allen, P. and Hummer, J. and Rouphail, N. and Milazzo, F.}, year={1998}, pages={87–95} }
 @inbook{rouphail_hummer_allen_1997, title={Bicycle operations and level of service literature synthesis}, booktitle={Final Draft, Federal Highway Administration, McLean, VA, January 1997}, author={Rouphail, N. M. and Hummer, J. E. and Allen, D. P.}, year={1997} }
 @inbook{fambro_rouphail_1997, title={Generalized delay model for signalized intersections and arterials}, ISBN={0309061504}, number={1572}, booktitle={Highway capacity issues and analysis}, publisher={Washington, DC: National Academy Press}, author={Fambro, D. and Rouphail, N.}, year={1997}, pages={112–121} }
 @book{rouphail_al._1997, title={ITS integration of real-time emissions data and traffic management systems}, publisher={Transportation Research Board}, author={Rouphail, N. M. and al.}, year={1997} }
 @article{tarko_rouphail_1997, title={Intelligent traffic data processing for ATIS applications}, volume={123}, DOI={10.1061/(ASCE)0733-947X(1997)123:4(298)}, abstractNote={Real-time traffic data are the lifeline sustaining the operation of Advanced Traffic Management and Advanced Traveler Information Systems (ATMS/ATIS). Data are essential to drive algorithms related to congestion/incident detection, travel time forecasting, and real-time route guidance. A common problem in many ATMS/ATIS applications is the sparsity of real-time traffic data, reflecting the financial constraints of acquiring and maintaining large-scale traffic monitoring systems. This paper proposes the use of intelligent processing, or data integration tools, to overcome the data sparsity problem and make the best use of existing data resources. This approach recognizes the elements of uncertainty and vagueness in defining and solving the problem. An example application of the proposed data integration method is presented in the context of a congestion detection algorithm. The method uses an imprecise knowledge representation within the framework of fuzzy operator logic (FOL) and the modified Dempster-Shafer rule of combination. Results indicate that knowledge of a link congestion status (i.e., congested or uncongested) increased several folds after the data integration algorithm was applied. Further work is needed to calibrate the algorithm in the field (in this study simulation was used) and to apply the procedures on large-scale networks.}, number={4}, journal={Journal of Transportation Engineering}, author={Tarko, A. and Rouphail, N.}, year={1997}, pages={298–307} }
 @inbook{rouphail_eads_1997, title={Pedestrian impedance on turning movements saturation flow rates: A comparison of simulation, analytical and field observations}, ISBN={0309061687}, number={1578}, booktitle={Pedestrian and bicycle research 1997}, publisher={Washington, DC: National Academy Press}, author={Rouphail, N. M. and Eads, B.}, year={1997}, pages={56–63} }
 @inproceedings{milazzo_rouphail_allen_hummer_1997, title={Proposed revisions to Highway Capacity Manual chapter 9: Pedestrian and bicycle analysis procedures}, booktitle={Proceedings of the ASCE Specialty Conference: Traffic Congestion and Safety in the 21st Century, Chicago, IL, June 8-11, 1997}, author={Milazzo, J. and Rouphail, N. and Allen, P. and Hummer, J.}, year={1997} }
 @article{ran_rouphail_tarko_boyce_1997, title={Toward a class of link travel time functions for dynamic assignment models on signalized networks}, volume={31}, ISSN={["0191-2615"]}, DOI={10.1016/S0191-2615(96)00036-7}, abstractNote={This paper investigates time-dependent travel time functions for dynamic assignment on signalized arterial network links. Dynamic link travel times are first classified according to various applications. Subsequently, stochastic and deterministic travel time functions for longer and shorter time horizons are discussed separately, and two sets of functions are recommended for dynamic transportation network problems. The implications of those functional forms are analyzed and some modifications for dynamic network models are suggested. In addition, based on dynamic link travel time functions, we discuss how many independent variables are necessary to describe the temporal traffic flow and properly estimate the time-dependent travel time and flow propagation over an arterial link. As a result, six link flow variables and corresponding link state and flow propagation equations are proposed as the basis to formulate dynamic transportation network models.}, number={4}, journal={TRANSPORTATION RESEARCH PART B-METHODOLOGICAL}, author={Ran, B and Rouphail, NM and Tarko, A and Boyce, DE}, year={1997}, month={Aug}, pages={277–290} }
 @inbook{engelbert_fambro_rouphail_1997, title={Validation of a generalized delay model for oversaturated conditions}, ISBN={0309061504}, number={1572}, booktitle={Highway capacity issues and analysis}, publisher={Washington, DC: National Academy Press}, author={Engelbert, R. and Fambro, D. and Rouphail, N.}, year={1997}, pages={122–130} }
 @inbook{rouphail_anwar_fambro_sloup_perez_1997, title={Validation of a generalized delay model for vehicle-actuated signals}, ISBN={0309061504}, number={1572}, booktitle={Highway capacity issues and analysis}, publisher={Washington, DC: National Academy Press}, author={Rouphail, N. M. and Anwar, M. and Fambro, D. and Sloup, P. and Perez, C.}, year={1997}, pages={105–111} }
 @inbook{nemeth_rathi_rouphail_1988, title={Traffic control at freeway work sites}, publisher={Civil Engineering Practice, N.J.: Technomic Publishing}, author={Nemeth, Z. and Rathi, A. and Rouphail, N.}, year={1988}, pages={211–231} }