@article{frey_choi_kim_2012, title={Portable emission measurement system for emissions of passenger rail locomotives}, DOI={10.3141/2289-08}, number={2289}, journal={Transportation Research Record}, author={Frey, H. C. and Choi, H. W. and Kim, K.}, year={2012}, pages={56–63} }
 @article{rasdorf_frey_lewis_kim_pang_abolhassani_2010, title={Field procedures for real-world measurements of emissions from diesel construction vehicles}, volume={16}, DOI={10.1061/(asce)is.1943-555x.0000027}, number={3}, journal={Journal of Infrastructure Systems}, author={Rasdorf, W. and Frey, C. and Lewis, P. and Kim, K. and Pang, S. H. and Abolhassani, S.}, year={2010}, pages={216–225} }
 @article{frey_kim_2009, title={In-use measurement of the activity, fuel use, and emissions of eight cement mixer trucks operated on each of petroleum diesel and soy-based B20 biodiesel}, volume={14}, DOI={10.1016/j.trd.2009.08.004}, number={8}, journal={Transportation Research. Part D, Transport and Environment}, author={Frey, H. C. and Kim, K.}, year={2009}, pages={585–592} }
 @article{lewis_rasdorf_frey_pang_kim_2009, title={Requirements and incentives for reducing construction vehicle emissions and comparison of nonroad diesel engine emissions data sources}, volume={135}, DOI={10.1061/(ASCE)CO.1943-7862.0000008}, number={5}, journal={Journal of Construction Engineering and Management}, author={Lewis, P. and Rasdorf, W. and Frey, H. C. and Pang, S. H. and Kim, K.}, year={2009}, pages={341–351} }
 @article{frey_kim_pang_rasdorf_lewis_2008, title={Characterization of real-world activity, fuel use, and emissions for selected motor graders fueled with petroleum diesel and B20 biodiesel}, volume={58}, DOI={10.3155/1047-3289.58.10.1274}, number={10}, journal={Journal of the Air & Waste Management Association}, author={Frey, H. C. and Kim, K. and Pang, S. H. and Rasdorf, W. J. and Lewis, P.}, year={2008}, pages={1274–1287} }
 @article{frey_rasdorf_kim_pang_lewis_2008, title={Comparison of real-world emissions of B20 biodiesel versus petroleum diesel for selected nonroad vehicles and engine tiers}, DOI={10.3141/2058-05}, number={2058}, journal={Transportation Research Record}, author={Frey, H. C. and Rasdorf, W. and Kim, K. and Pang, G. H. and Lewis, P.}, year={2008}, pages={33–42} }