How Does Eco-Routing Affect Total System Emissions? City Network Predictions From User Equilibrium Models

Transportation contributes a substantial fraction of all greenhouse gas emissions. One approach for reducing such emissions is to modify vehicles’ route choices to minimize their fuel consumption or emission, which is known as eco-routing. Most eco-routing is based on vehicles choosing routes that minimize their individual fuel consumption or emissions. The Braess paradox demonstrates that when vehicles choose routes to minimize their individual goals, the aggregate effect may paradoxically result in the opposite net effect due to changes in congestion patterns. We construct a multiclass user equilibrium model in which some vehicles use eco-routing and others seek to minimize their individual travel times. Using this model, we show that the Braess paradox exists for eco-routing. If a large number of vehicles is trying to minimize their fuel consumption or emissions, the total fuel consumption or emissions may increase. We then solve the multiclass user equilibrium on publicly available city network data, and find that eco-routing results in increases in fuel consumption and emissions on some city networks as well.