Downtown tolls and the distribution of trip lengths

Currently, all downtown tolls are “access tolls,” meaning they charge for gross access to a zone, but tolls levied on distance-traveled are on the horizon. This paper shows how such tolls affect the distribution of trip lengths. A static model is presented in which travelers with potentially different trip lengths decide whether to drive into a downtown zone governed by a Macroscopic Fundamental Diagram (MFD), with each traveler's choice probability declining as tolls and travel time rise. An application of Little's Law allows the model's equilibria to be derived in terms of a familiar supply/demand framework. Analysis proves and numerical simulation demonstrates that, if trip lengths and the value of a trip both vary across travelers, then access tolls inefficiently shift the distribution of car trip lengths toward long trips, whereas a distance toll can achieve the welfare-maximizing set of car trips.