Intelligent cruise control (ICC) vehicles are already commercially available in Japan and should be ready for the North American market by next year. Although the controllers are local and string stable, it is not clear how the vehicles perform environmentally. It is shown that ICC vehicles can accurately track a lead vehicle and attenuate position errors generated by the lead vehicle during smooth transients. Furthermore, the smooth response of ICC vehicles designed for human factor considerations filters out traffic disturbances caused by rapid acceleration transients. Such ICC vehicle properties have beneficial air pollution and fuel consumption effects that are significant when the manual vehicles perform aggressive rapid acceleration maneuvers. These results are obtained using the Pipes human driver vehicle following model, which models the slinky-type effects observed in today's manual driving. The response of the Pipes model is compared with that of human drivers. The Pipes model is observed to give a smooth approximation of human driver response during transients. Simulations have demonstrated that the fuel consumption and pollution levels present in manual traffic can be reduced during rapid acceleration transients by 28.5% and 1.5 to 60.6%, respectively, by the presence of 10% ICC vehicles. Experiments with actual vehicles are used to validate the theoretical and simulation results.