The potential fuel economy and exhaust emission benefits that might be obtained by smoothing the flow of traffic have been investigated. Substantial improvements in fuel economy and reductions in exhaust emissions are possible if the flow of traffic is smoothed. Traveling during the smooth flow conditions of the early morning (4 am) as compared to travel on the same urban route during highly congested flow (5 pm rush hour) resulted in a fuel economy improvement of 31% for hot-starts and 35% for cold-starts. Also, traveling during smooth flow conditions resulted in reductions in HC, CO, and NOx emission levels of 54%, 52%, and 2% respectively for hot-starts and 35%, 52%, and 13% respectively for cold-starts. The reported results were obtained by simulating traffic conditions on a chassis dynamometer.