Building More Roads Does Not Ease Congestion

As former mayor of Bogota, Enrique Peñalosa, said, "Trying to solve traffic problems by building more roads is like putting out a fire with gasoline." Photo by Joe Wolf.

Congestion is not an easy beast to tame for cities around the world. Building more roads and increasing the capacity of public transport does little to improve congestion, according to new research conducted in American cities and published by economists at the University of Toronto. The authors expand upon the classic “law of peak-hour traffic congestion,” published by Anthony Downs in 1962, which states that “on urban commuter expressways, peak-hour traffic congestion rises to meet maximum capacity.” The University of Toronto researchers believe that the law can be applied to all major urban roads, not just expressways. Drivers in São Paulo, Beijing and Los Angeles would likely agree.

Despite this research, many cities are still trying to relieve congestion and accommodate higher rates of car ownership by building even more roads exclusively for cars. But as the former mayor of Bogota, Enrique Peñalosa, said, “Trying to solve traffic problems by building more roads is like putting out a fire with gasoline.”

The main issue is the intense demand for space on roads. When a new space is opened, either by building new roads or incentivizing drivers to switch to public transport, the road space vacated is soon occupied by more cars. The provision of more road space does nothing to diminish the underlying demand causing the congestion.


The researchers conclude that the only effective way to combat congestion is through pricing schemes. The idea has been rejected in the United States and elsewhere, despite widely reported successes in cities like London and Stockholm, where implementation of congestion pricing has produced reductions in car traffic of up to 30 percent, not to mention other successful case studies in Singapore and Milan.

The largest hurdles to implementation are political. The most famous congestion pricing defeat was in New York City, where Mayor Michael Bloomberg tried to implement a congestion charge only to see it rejected by the state legislature in Albany.

The proposal to politicians and to the public has to be made in clear terms. Congestion has enormous economic, health and environmental costs. These costs are often underestimated or misunderstood. Congestion pricing is not just the only proven tool to reduce traffic congestion, but it can also save cities billions of dollars in health costs and lost economic productivity, as well as improve cities’ competitiveness and environmental quality.

This post was based on a post by Eric Jaffe, contributing writer for Place Matters, produced by The Atlantic Cities. The blog, which is only about one month old, has quickly become a must-read for people who care about cities. The blog is primarily focused on American cities, and it also includes posts about cities around the world, like this one on public space in slums and this one on social housing in Mexico. Check it out!

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