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Public Radio's Environmental News Magazine (follow us on Google News)

More Roads, More Traffic

Air Date: Week of

It sounds like a Buddhist koan - more roads means more traffic - but Professor Matthew Turner of the University of Toronto calls it the Fundamental Law of Road Congestion. He explains to host Jeff Young that even though we spend billions expanding roads and adding transit, neither will affect congestion.


YOUNG: Summer, the season synonymous with the American Road Trip is also known for gridlock. And when you’re stuck in traffic – maybe you are right now - you might wish for wider roads. But a new paper in the American Economic Review warns: careful what you wish for. Here to explain is University of Toronto Professor, Matthew Turner - a true roads scholar - who studied what’s known as "the fundamental law of road congestion." Professor Turner, what happens when we build more high ways - we all drive free and happy as the automotive gods intended, right?

TURNER: Well, that’s actually not quite what happens!

YOUNG: (Laughs.)

TURNER: What we find is that traffic or driving increases almost one for one with the amount of roads. So if you build it they will come, if you add one percent more roads to a city, you’ll see almost exactly one percent more driving.

YOUNG: So we can’t pave our way out of traffic?

TURNER: You can’t pave your way out of traffic.

YOUNG: Why is that what happens when we build those extra roads?

TURNER: Well, there seem to be three main contributors. As you build more roads in a city, people change their behavior, so they’ll take…they’ll drive more. They’ll take another trip to the store; they’ll commute a little bit further. That seems to be the biggest reason for this. There also seems to be a big response in trucking, so as you build more roads, there will be a big increase in the amount of trucking in the city. And finally, people migrate to cities with more roads. If you add ten percent to the city’s road network, then you’ll see about one and a half percent increase in population over 20 years.

YOUNG: You’ve got some very interesting data in the study here - you compared the amount of time that we Americans were spending in cars in 2001 to data from 1995. And just in that short time period, you found…what?

TURNER: We found that people were driving about 20 percent more, spending about 20 percent more time in their cars to accomplish the same amount of driving. When I started doing this, I had no idea how important driving was to the American economy. If you look at the numbers for, on the order of one dollar in six that the average households spends, is spent on cars or driving. They spend three hours per day in the car.

YOUNG: Well, what about public transit - what if instead of building the new lanes on highways we built more bus routes, more rails, things like that?

TURNER: Well, what we found is that if you add capacity to the road network, then people use it. What public transit does, is it adds transportation capacity. What we find is that if you take someone off a road and put them on a bus or on a light rail system, then someone takes their place. So adding transit is just like adding capacity. It doesn’t affect the level of travel on the existing roads. So the short story is that as you build transit, it doesn’t reduce the amount of driving.

YOUNG: So, if pavement is not the answer, public transit is not the answer, where should we be looking for answers? Because we’ve got this traffic problem, what should we be doing about it?

TURNER: Oh boy, well that’s exactly the right question to be asking. So the saddest response that we have to congestion is really quite small - it’s capacity increases, public transit increases and congestion pricing.

YOUNG: What is congestion pricing?

TURNER: Congestion pricing is when you charge people for the right to use the road at particular times and in particular places where the roads are crowded. And this is something which has been tried in a number of cities around the world: Singapore, London and Stockholm are the big examples. Well, the tolls to get into Stockholm are on the order of 0.50 cents or two dollars a day, and they’re seeing 100 percent increases on speed on congested arterial roads.

A congestion charge on Old Street into London has helped stave off traffic jams. (wikimedia)

YOUNG: Another thing I like about your study is, you know, we read a lot of studies that are worded in very wishy-washy ways. You cut right to the chase: You propose a law of road congestion that says: “Adding road capacity will not alleviate congestion on any sort of major urban road or rural highway within metropolitan boundaries.” It’s just like that. You’re pretty sure of this.

TURNER: Well, we think it’s pretty ambitious. I’ve been in this business for a long time now and I have never seen empirical results which were as unequivocal as the ones that we find. And, I’m pretty excited about that - facts are scarce in the social sciences and I think we may have found one.

YOUNG: Professor Matthew Turner teaches economics at the University of Toronto. His paper is in the upcoming issue of American Economic Review. Thanks very much!

TURNER: Thank you for having me on the show.




Turner's Paper


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