Hyperdemand: A static traffic model with backward-bending demand curves. (December 2020)

• Record Type: Journal Article
• Authors: Lehe, Lewis J.; Pandey, Ayush
• Is Part Of: Economics of transportation. Volume 24(2020)
• Publication Date: 2020-12
• Subjects: Carpool -- Toll -- Macroscopic fundamental diagram -- Isotropic -- Congestion -- Ridesharing; Transportation -- Periodicals; 388.049
• DOI: 10.1016/j.ecotra.2020.100182
• Languages: English
• ISSNs: 2212-0122

Abstract

Abstract: Static traffic models, in the tradition of Walters (1961), typically feature a ''demand curve'' giving the vehicle flow demanded for each unit travel time (inverse speed). Traditionally, the demand curve declines because people want to drive more as travel times fall. This paper proposes that the vehicle flow demanded can, instead, plausibly rise with unit travel time (a phenomenon we call ''hyperdemand''), if congestion somehow induces some people to switch from high-to low-occupancy modes. To illustrate, we present a model of travel in an isotropic downtown where people choose among not traveling, a low-occupancy mode called ''Alone'' and a high-occupancy mode called ''Pool.'' Pool trips detour to pick up and drop off passengers en route, so congestion delays them more than Alone trips. Consequently, multiple equilibria can arise even in ''light congestion, '' and small toll increases can have dramatic impacts by eliminating equilibria. Highlights: Derives a static traffic model in which vehicle flow demanded rises with congestion. Multiple equilibria can occur in light congestion. Small changes to tolls can have dramatic effects by eliminating equilibria. Temporary tolls can have permanent effects on congestion.