Adding more road capacity decreases congestion and increases distance traveled

Three lines of oncoming traffic are depicted moving at a very slow rate in three congested lanes. The opposite lane appears to move quickly.

Traffic congestion on urban roads is increasing worldwide. Theories discussed in this paper offer promising results about the benefits of widening roads. 

By Peter Murphy

Published January 10, 2023

Study confirms widening roads will reduce travel delays, lower congestion, and could, increase the number of kilometers traveled. 


Alex Anas, Frank H. and Josephine L. Goodyear Professor, Department of Economics chair and Stephen Still Institute of Sustainable Transportation and Logistics (Stephen Still ISTL) affiliated faculty member presented his paper Downs’s Law under the lens of theory: Roads lower congestion and increase distance traveled during the Conference on Urban and Regional Economics at the Singapore Management University – Jinan.

Research in this paper, according to Anas, uses theoretical economic models to examine both the direct and indirect effects of increasing road space.

Alex Anas.

Alex Anas, Frank H. and Josephine L. Goodyear Professor

“Traffic congestion on urban roads is increasing worldwide, and the most congested cities are in developing countries, closely followed by major European capitals and large U.S. cities,” Anas says. “In this paper, a series of theoretical economic models are developed which help to examine not only the direct effects of adding more road capacity, but also, the indirect effects of road capacity on rents, incomes, the value of time, consumption-linked trips, road costs, spatial detail, and other factors. In each case, it is proved that, after including these indirect effects, adding more road capacity lowers congestion.”

In the paper, Anas demonstrates that increasing road capacity lowers congestion by measuring delays in travel. Reduced congestion, according to Anas, induces more travel, which can, but does not always, lead to more distance traveled.

The research builds upon the predictions of American economist Anthony Downs from 1962. The paper, while purely theoretical, could have a significant impact on the debate surrounding widening roads and its effect on traffic congestion.

“There has been a controversy, and this paper should improve confidence that more roads do reduce congestion and would hopefully influence others to examine the issue further,” Anas says.