Integration Modeling Framework for Estimating Mobile Source Emissions

Transportation network improvements are commonly evaluated by estimating average speeds from a transportation/traffic model and converting them into emission estimates using an environmental model such as MOBILE or EMFAC. Unfortunately, recent research has demonstrated that average speed, and perhaps even simple estimates of the amount of delay and the number of vehicle stops on a roadway, is insufficient to fully capture the environmental impacts of Intelligent Transportation System (ITS) strategies such as adaptive traffic signal control. Specifically, for the same average speed, one can observe widely different instantaneous speed and acceleration profiles, each resulting in very different fuel consumption and emission levels. In an attempt to address this limitation, the paper presents the INTEGRATION model framework for quantifying the environmental impacts of ITS alternatives. The model combines car-following, vehicle dynamics, lane changing, energy, and emission models to estimate mobile source emissions directly from instantaneous speed and acceleration levels. The validity of the model is demonstrated using sample test scenarios that include traveling at a constant speed, traveling at variable speeds, stopping at a stop sign, and traveling along a signalized arterial. The study also demonstrates that an adjustment in driver aggressiveness can provide environmental benefits that are equivalent to the benefits of adaptive traffic signal control.