Environmental Traffic Assignment: Developing Emission-based Models

Vehicle tailpipe emissions are major sources of air pollution and greenhouse gases. In addition to the ongoing efforts on emissions reduction, we believe there is a need to explore an innovating approach in which drivers routing decisions are influenced to minimize emissions and fuel consumption. In order to evaluate such transportation systems, we develop environmental traffic assignment models (E-TA) based on user equilibrium (UE) and system optimal (SO) behavioral principles. Extending the traditional travel time based UE and SO principles to E-TA is not straightforward because, unlike travel time, vehicle emissions increase with the increase in vehicle speed beyond a certain point. The results of various TA models show a network-wide traffic control strategy in which vehicles are routed according to SO based E-TA, can reduce system wide emissions. However, a system in which drivers make routing decisions to minimize their own emissions, (E-UE system) results in increased individual as well as systemwide emissions.