A quick drive on one of Los Angeles's many freeways illustrates the fact that having more roads doesn't necessarily prevent traffic. Now a study from the University of Toronto confirms it: Expanding highways and roads increases congestion by creating more demand. And building out public transportation systems doesn't help either; there will always be more drivers to fill up any new road we build.
The disheartening study used data from hundreds of metro areas in the U.S. to reach the conclusion that there is a "fundamental law of highway congestion," which essentially says that people drive more when there are more roads to drive on--no matter how much traffic there is. As a result, increased building of "interstate highways and major urban roads is unlikely to relieve congestion of these roads."
Not even building more trains, buses, and light rail can help with the traffic problem. In an interview with Streetsblog, study coauthor Matthew Turner explains that his fundamental law means that people are always waiting for extra space on the roads, and a person taking the bus simply opens up space for a new car:
If somebody stays home, or if you add capacity to the road, there’s somebody there waiting to use that space. Well you should expect the same thing to happen if somebody gets out of their car and gets on the bus, it’s bringing up a little bit more room on the roads, and there’s somebody out there waiting to use it.
This doesn't mean public transportation is worthless; it transports more people with less fuel and fewer carbon emissions. But spending more on it has no effect on traffic.
So what does help? The University of Toronto researchers offer just one suggestion: congestion pricing. It's a pain for commuters, but that's sort of the point. People are desperate to drive, so if you want less traffic, you have to make it harder for them.