道路越多可能交通流量越多

GUY RAZ, host: Next weekend, Carmageddon will hit Los Angeles. The city will close one of its main freeways, the 405, for 53 hours from Friday night to Monday morning. It's part of a billion dollar project to widen the freeway that city planners hope will ease chronic congestion on the 405.

But according to new research by an economist at the University of Toronto named Matthew Turner, that project, well, it will actually make traffic worse. Turner and a colleague studied traffic in 228 U.S. cities and determined that the more roads you build, the more congestion you create.

MATTHEW TURNER: And what we found was that in cities where there was more roads, there was more driving. In particular, if you had 1 percent more roads, you had 1 percent more driving in those cities.

RAZ: One interesting thing I read in your study is about public transportation. Again, counterintuitive. You would think that the more public transportation that's built in a city, the more impact it would have on easing congestion. Here in Washington, D.C., as you probably know, we've got the Beltway around the city. It's notorious for traffic snarls（美国口语---traffic jams). There's great public transit in this city, people have that option. But, in fact, you say it doesn't always help either.

TURNER: What we find is that as you increase, say, the stock of light rail or bus cars, that there's no impact on the amount of driving. And that sounds sort of surprising, but it's logically consistent with the other result that we have about the effect of roads on driving. What we find is that as you add roads to a city, those roads get filled up. So there are people waiting to use that capacity. The result on transit is almost exactly the opposite of that.

RAZ: So it's almost like there's a long line of people waiting to use that space on the freeway. The minute you put somebody in a bus or a metro train, someone else is just going to take their space on the roads.

TURNER: I think that's right. I think there's a lot of people out there trying to decide whether to make one more trip to the store or drive a little further to work. And as you add, a little bit more capacity, it gets filled up.

RAZ: So now, this is going to sound very frustrating to, you know, smart mayors all across America because they're going to sort of listen to this and say: What can I possibly do to ease congestion if I can't build more roads or I can't, you know, build more public transit? What can I do?

TURNER: We have really a small number of possible policy responses to congestion. One is capacity increases, one is transit increases and the third is congestion pricing. And what we've shown is that the first two of those policy responses are unlikely to work, which leaves congestion pricing.

RAZ: This is essentially charging people to drive into a city or to use a road, tolls.
TURNER: That's exactly right, much in the same way as they do in London or Singapore or Stockholm.

RAZ: In London, I think it costs about 10 pounds to go into the city. And Mayor Bloomberg in New York actually had that idea, right? He wanted to charge a fee for people to drive into the city, but it was a nonstarter.

TURNER: And the reason it's a nonstarter, I think, is that people don't want to pay for something that they're used to having for free, which is completely reasonable. However, we have enough experience with these programs now to know that in fact, they really work. In response to pretty small fees, you see big reductions in travel time. So in Stockholm, the tolls to get into the city on the order of a couple of dollars, and they saw 50 percent reductions in travel time at peaks.

RAZ: If you had a congestion charge to get into a city, wouldn't it naturally have a greater impact on people who might not necessarily be able to afford paying that charge?

TURNER: I think the answer to that is yes. And that a concern with congestion charges is that they fall more heavily on the poor for whom travel is a bigger share of their budget and who tend to have less discretion about when they go to work. I think the way you want to think about this is that road infrastructure and transportation infrastructure is fantastically expensive to build. And what we want to do is want to organize the way we use these assets so that we use them to their best advantage, right? And that may mean that some people move to different cities. It may mean that some people change the time when they go to work.

We can anticipate all the different margins of adjustment. Some of them will be painful for people and some of them will not be.

RAZ: That's Matthew Turner. He is a professor of economics at the University of Toronto and a visiting fellow at the Property and Environment Research Center in Bozeman, Montana. Matthew Turner, thank you.

TURNER: Thank you very much for having me on your show.