Toronto politicians have long described transit as a “decongestant” because buses, streetcars and subways get people out of their cars. But a new study on driving patterns in American cities, released recently by a pair of U of T economists, suggests that adding transit service doesn’t relieve traffic gridlock in the long term.
The research, by Gilles Duranton and Matthew Turner, expands on a long-observed phenomenon: that adding highway capacity doesn’t reduce traffic congestion and the additional lanes just fill up over time. The main reason: individuals change their driving behaviour, triggering even more traffic. “Build it,” says Turner, “and they will drive.”
The Fundamental Law of Road Congestion
Adding transit doesn’t short-circuit traffic buildup either, Turner concludes. Drivers that give up their cars for transit are eventually replaced by new drivers. But he notes the study shouldn’t be interpreted as a case against transit because the provision of additional buses, in particular, allows more people to take trips on existing transportation infrastructure at little extra cost.
Duranton and Turner calculate the benefits drivers gain from new roads in the U.S. and conclude that they are well below the cost of providing the roads. Extending subways and streetcar routes are also expensive and result in little gain for the average commuter.
So what is the best public policy response to gridlock? The authors suggest that the City of London has the right idea, using peak-hour traffic tolls to dissuade drivers from taking their cars to work. “These findings strengthen the case for congestion pricing as a policy response to traffic congestion,” their report concludes.
The study was published by the National Bureau of Economic Research.