Public Transportation Does Relieve Traffic Congestion, Just Not Everywhere

The idea that public transportation relieves road congestion is both logical and popular, but the evidence for it is decidedly mixed. The "fundamental law of road congestion," for instance, suggests that transit fails to relieve traffic because latent demand for road space is so great. (The only hope of reducing congestion, according to this work, is establishing road fares.) So while there are any number of reasons to support the public funding of public transportation — sustainability, for instance, or social welfare — economists don't all find congestion relief to be one.

That debate just got a lot more interesting with some new work (via Paul Krugman) by Berkeley scholar Michael Anderson, who argues that "the net benefits of transit systems appear to be much larger than previously believed." By analyzing the impact of a Los Angeles transit strike in 2003, Anderson found that congestion did decrease considerably — but only on roads that paralleled heavy transit corridors. He suggests that previous research has focused too much on general metro traffic and not enough on the specific roads that transit is most likely to influence: