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Building New Roads Increases Traffic
Does not help congestion
Jay Blazek Crossley, Jun 06, 11.
Building new roads does not reduce congestion for metropolitan regions and can actually increase traffic, according to an upcoming report to be published in the American Economic Review, as explained in Streetsblog Capital Hill.
The report also notes that transit is not an appropriate tool for the auto-based problem of combating congestion, while congestion pricing is the “main candidate tool to curb traffic congestion.” The researchers looked mostly at building new roads and transit, but are conducting research now on the potential of the fourth major available tool for reducing congestion: smart growth.
Professors Gilles Duranton and Matthew Turner analyzed travel data from hundreds of metro areas in the US, resulting in what they call the most comprehensive dataset ever assembled on the traffic impacts of road construction. They write:
For interstate highways in metropolitan areas we find that VKT [vehicle kilometers traveled] increases one for one with interstate highways, confirming the “fundamental law of highway congestion” suggested by Anthony Downs (1962; 1992). We also uncover suggestive evidence that this law may extend beyond interstate highways to a broad class of major urban roads, a “fundamental law of road congestion”. These results suggest that increased provision of interstate highways and major urban roads is unlikely to relieve congestion of these roads.
Duranton and Turner say building more roads results in more driving for a number of reasons: People drive more when there are more roads to drive on, commercial driving and trucking increases with the number of roads, and, to a lesser extent, people migrate to areas with lots of roads. Given that new capacity just increases driving, they find that “a new lane kilometer of roadway diverts little traffic from other roads.”
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The implications for this research are significant, especially as Congress considers whether to integrate performance measures into federal transportation spending decisions. These findings make a strong case that Congress should not allocate too many scarce resources to road expansion when that’s not a real solution for congestion.
Duranton and Turner say that metropolitan areas tend to get new roads regardless of whether or not the prevailing level of traffic warrants expansion. They urge the establishment of transportation policies based on their findings and the data they compiled, rather than the “claims of advocacy groups”:
Unfortunately, there is currently little empirical basis for accepting or rejecting the claims by the American Road and Transportation Builders Association that “adding highway capacity is key to helping to reduce traffic congestion”, or of the American Public Transit Association that without new investment in public transit, highways will become so congested that they “will no longer work”. Our results do not support either of these claims.
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“The menu of policy responses to congestion is not really that long,” Turner said in our interview. “You’ve got building more roads, building more transit, and congestion pricing, and if you’d like you can put smart growth on there. We looked at two of those really carefully and found that they didn’t perform as advertised. So if you’re thinking about these things purely as responses to congestion, it doesn’t look like they work. There is some evidence that congestion taxes work. So if you were going to pick one of these things to go for, that would be it.”
They’re working on research now to investigate the impacts of smart growth on
traffic.
(back to me)
This is pretty interesting stuff. Of course, it makes sense - it's something that planners and transportation folks have known for a long time. Construction of new roads designed to relive congestion do not have that effect long-term. The scenario runs like this:
1. A road is built.
2. Businesses, homes, etc are built using that road as an access.
3. The businesses are successful attracting more folks.
4. These folks get there by driving, impacting the road.
5. The roadway is expanded, with resulting (short-term) decrease in congestion.
6. Eventually the cycle will reach the point where it is not feasible to expand the roadway further.
7. A new roadway is built with the goal of relieving traffic on the now fully-expanded road.
8. Return to step 1.
Roadways are EXPENSIVE. Not only to construct - our Eagle Drive improvements are just for construction and have run to costs in excess of $16 million - but to acquire right of way costs a lot of money. Particularly when people are savvy and know the project must be built. Money spent on regional transportation options in addition to local transit options is much more efficient and actually has a greater impact on roadway congestion than additional roadways do.
Maybe it's a good think TxDOT is broke...
