The Institute of Transportation Studies at the University of California, Davis (ITS-Davis) has brought together a group of public and industrial partners to demonstrate and evaluate the Siemens-Westinghouse Urea-Selective Catalyst Reduction System (SINOx TM). The SINOx System has the potential to generate major reductions in nitrogen oxides (NOx) and the volatile organic fraction (VOF) of particulate (PM) from heavy-duty diesel engines, without increasing fuel consumption and carbon dioxide (CO2) emissions. This demonstration began with engine bench testing at Detroit Diesel Corporation to calibrate the system to attain 1 g/bhp-hr NOx emissions in the transient portion of the US-FTP on a 1999 Series 60 engine that has a 4 g/bhp-hr emission level. The second phase of the project entails an on-highway demonstration of a set of ten, Freightliner Class 8 heavy-duty diesel vehicles. These vehicles are part of the Valley Material Transport fleet based in French Camp, California Performance of the SINOx System will be tested under realistic on-road operating conditions, using on-road emissions measurement techniques as well as traditional dynamometer testing. In addition to emissions and fuel economy testing, a comprehensive study will investigate trucking industry acceptance, infrastructure needs, technical feasibility, and cost-effectiveness of the system. This evaluation is funded by San Joaquin Valley Unified Air Pollution Control District, Sacramento Air Pollution Control District, and California Air Resources Board.