In view of the major contribution that vehicular emissions make to urban air quality, governments around the world have enacted legislation designed to reduce vehicle emissions. Developed countries have implemented increasingly stringent emission standards that have forced technological advances or
responded to available, proven technology. The reductions in emissions are due to improvements in vehicle technology and fuel properties. The influences of vehicle technology and fuel composition on emissions are complex and interdependent. This report focuses on the effect of engine and vehicle
technology changes as they affect vehicle emissions.