A dynamic traffic-flow model (DTFM) is used in this study to evaluate the effectiveness of introducing electric vehicles (ET's) into the total traffic system as one of the alternative fuel vehicles. This model simulates congested and non-congested traffic flow caused by changes in the traffic demand. An environmental evaluation is carried out on the basis that all vehicles are substituted for EVs. Calculated results indicate that by introducing EVs, the NOx, emissions and the CO2 emissions can be reduced by approximately 25.7 and 14.4% respectively. If battery performance of EVs is improved further, emissions can be further reduced by 39.6% (NOx) and 27.8% (CO2). Since emissions from heavy-duty vehicles are greater than other vehicles, the following measures have to be taken for these vehicles to significantly improve their impact upon the overall environment: (1) improvement in fuel efficiency and reductions of NOx in exhaust gas, (2) traffic demand management, such as modal shift.