U of T study finds road expansion increases traffic by increasing demand

Thursday, June 23, 2011 10:02:00 AM

Research and Publication News


New article: Gilles Duranton and Matthew A. Turner.  The Fundamental Law of Road Congestion: Evidence from US cities.  American Economic Review. (Forthcoming.) Available free online.


Using a more comprehensive dataset than previous similar traffic studies, this paper analyzed city level traffic in the continental United States between 1983 and 2003.  The study confirms the existing "fundamental law of highway congestion" where the extension of interstate highways is met with a proportional increase in traffic in the U.S (Anthony Downs, 1962; 1992). This law finds that people drive more when the stock of roads in their city increases, commercial driving and trucking increase with a city's stock of roads and people migrate to cities which are relatively well provided with roads. The study finds evidence that this law may extend beyond interstate highways to a broad class of major urban roads, that is, a "fundamental law of road congestion".  The data also suggests that a new lane kilometer of roadway diverts little traffic from other roads.  Interestingly, the study also found no evidence that public transit affects the number of kilometres travelled by vehicles. These findings suggest that both road capacity expansions and extensions to public transit are not appropriate policies with which to combat traffic congestion and suggest congestion pricing as the main candidate tool to curb traffic congestion.

The article above was compiled from edited excerpts from the article by Duranton and Turner.

References cited:
Downs, Anthony. 1962. The Law of Peak-Hour Express-Way Congestion. Traffic Quarterly 16(3): 393-409.

Downs, Anthony. 1992. Stuck in Traffic: Coping With Peak-Hour Traffic Congestion. Washington D.C.: Brookings Institution Press.

Gilles Duranton is Professor and Noranda Chair in Economics and International Trade, Dept. of Economics, University of Toronto; more information: http://individual.utoronto.ca/gilles/default.html

Matthew Turner is Professor, Dept. of Economics, U of T; more information: http://homes.chass.utoronto.ca/~mturner/index.htm