Neither roads nor public transit will help?
In the October 2011 issue of the American Economic Review, authors Gilles Duranton and Matthew A. Turner review traffic data from the years 1983 to 2003. Their article, “The Fundamental Law of Road Congestion: Evidence from US Cities,” finds that, for the time period reviewed, congestion continues regardless of whether more roads or public transit were added. Their abstract:
“We investigate the effect of lane kilometers of roads on vehicle-kilometers traveled (VKT) in US cities. VKT increases proportionately to roadway lane kilometers for interstate highways and probably slightly less rapidly for other types of roads. The sources for this extra VKT are increases in driving by current residents, increases in commercial traffic, and migration. Increasing lane kilometers for one type of road diverts little traffic from other types of road. We find no evidence that the provision of public transportation affects VKT. We conclude that increased provision of roads or public transit is unlikely to relieve congestion.”
Have trends since that time – a flattening of VKT and an increase in transit ridership – altered that conclusion?