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- Hu, J.; Frey, H. C.; Sandhu, G. S.; Graver, B. M.; Bishop, G. A.; Schuchmann, B. G.; Ray, J. D. Method for Modeling Driving Cycles, Fuel Use, and Emissions for Over Snow Vehicles. Environmental Science & Technology, 48 (14): 8258–8265, 2014. Link.
- Sandhu, G.S.; Frey H.C. Effects of Errors on Vehicle Emission Rates from Portable Emissions Measurement Systems. Transportation Research Record: Journal of the Transportation Research Board of the National Academies, 2340: 10-19, 2013. Link.
- Boroujeni, B.Y.; Frey, H.C.; Sandhu, G.S. Road Grade Measurement Using In-Vehicle, Stand-Alone GPS with Barometric Altimeter. Journal of Transportation Engineering of the American Society of Civil Engineers, 139 (6): 605–611, 2013. Link.
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