“Downs's Law” Under the Lens of Theory: Roads Lower Congestion and Increase Distance Traveled

47 Pages Posted: 20 Jan 2023 Last revised: 21 Jan 2024

See all articles by Alex Anas

Alex Anas

State University of New York at Buffalo

Date Written: October 16, 2023


Downs (1962) claimed a “Law”: that expressways lower congestion even though they reach maximum traffic flow. In urban economics since Strotz (1965), road capacity is measured by road width, and congestion as the delay in travel: wider roads lower congestion. Duranton and Turner (2011), in an econometric study, atypically defined congestion, not as delay in travel, but as aggregate vehicle kilometers traveled (VKT) relative to the aggregate length of roads, concluding that roads are unlikely to relieve congestion. We first provide the theory behind “Downs’s Law”. Then, in a series of theoretical models, we endogenize rent, income, the value of time, leisure, Marshallian productivity, consumption-linked trips, road costs, spatial detail, and a suburb-to-city expressway competing with existing roads. In each case we prove that adding more road capacity lowers congestion and increases utility in the short run when city population is fixed; and lowers congestion in the long run too despite induced travel or population growth. Aggregate travel cost and VKT rise or fall, depending on how much congestion is lowered, on the cost elasticity of travel demand, on location-based income and substitution effects, and on which roads are widened.

Keywords: Congestion theory, Road capacity, Vehicle miles traveled, Aggregate travel cost, Urban general equilibrium

JEL Classification: D00,R00

Suggested Citation

Anas, Alex, “Downs's Law” Under the Lens of Theory: Roads Lower Congestion and Increase Distance Traveled (October 16, 2023). Available at SSRN: https://ssrn.com/abstract=4331232 or http://dx.doi.org/10.2139/ssrn.4331232

Alex Anas (Contact Author)

State University of New York at Buffalo ( email )

Amherst, NY 14260
United States
17162289908 (Phone)

HOME PAGE: http://https://sites.google.com/site/alexanashomepage/

Do you have negative results from your research you’d like to share?

Paper statistics

Abstract Views
PlumX Metrics