Saturday, April 01, 2006
The Induced-Driving Myth
Do new highways merely "induce" more driving? Or is that just an excuse for not building any and letting cities become even more congested?
Robert Cervero is a planning professor at the University of California (Berkeley) who supports New Urbanism and transit-oriented developments. But he is also an honest researcher. So when he looked at the idea of induced travel, he concluded that previous studies "suffered from methodological problems that distorted their findings," such as by confusing cause and effect.
Cervero's own research shows that "for every 100 percent increase in capacity," new development leads to about a 40-percent increase in traffic. This is "substantially less than reported by past induced-demand studies" and shows that new construction can lead to a reduction in congestion.
"Fighting highway projects, regardless what benefit-cost numbers say, is misguided," concludes Cervero. "The problems
people associate with roads—e.g., congestion and air pollution—are not the fault of road investments per se. These problems stem from the use and mispricing of roads, new and old alike."
Part of the problem is that highway construction today is so delayed by planning studies and processes that, by the time any road gets built, the demand for that road has already exceeded its capacity. For example, Minnesota did a study of highway 10, a four-lane road north of Minneapolis, and found that by the time it could build two new lanes, traffic will have grown by more than 50 percent. Thus, the road at completion would be more congested than it is today -- not because of induced demand but simply because of the normal growth in traffic. This does not mean we should not build roads, only that we should speed up the process.
Robert Cervero is a planning professor at the University of California (Berkeley) who supports New Urbanism and transit-oriented developments. But he is also an honest researcher. So when he looked at the idea of induced travel, he concluded that previous studies "suffered from methodological problems that distorted their findings," such as by confusing cause and effect.
Cervero's own research shows that "for every 100 percent increase in capacity," new development leads to about a 40-percent increase in traffic. This is "substantially less than reported by past induced-demand studies" and shows that new construction can lead to a reduction in congestion.
"Fighting highway projects, regardless what benefit-cost numbers say, is misguided," concludes Cervero. "The problems
people associate with roads—e.g., congestion and air pollution—are not the fault of road investments per se. These problems stem from the use and mispricing of roads, new and old alike."
Part of the problem is that highway construction today is so delayed by planning studies and processes that, by the time any road gets built, the demand for that road has already exceeded its capacity. For example, Minnesota did a study of highway 10, a four-lane road north of Minneapolis, and found that by the time it could build two new lanes, traffic will have grown by more than 50 percent. Thus, the road at completion would be more congested than it is today -- not because of induced demand but simply because of the normal growth in traffic. This does not mean we should not build roads, only that we should speed up the process.
Comments:
After reading the article, Cervero's analysis is simply hair-splitting.
If auto travel was priced to "internalize ALL the externalities" (even if limited to the ones we can measure directly), in principle, urban motor travel volumes would drop about 40% to 50% (and transit would increase 4 or 5 fold). Under such conditions, we could tear out a lot of existing freeways, particularly in central areas where they've caused the most damage in the first place.
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If auto travel was priced to "internalize ALL the externalities" (even if limited to the ones we can measure directly), in principle, urban motor travel volumes would drop about 40% to 50% (and transit would increase 4 or 5 fold). Under such conditions, we could tear out a lot of existing freeways, particularly in central areas where they've caused the most damage in the first place.
