Tuesday, September 27, 2011

Congestion, part 2

The Texas Transportation Institute has issued its 2011 report on traffic congestion. Although TTI changed its methodology somewhat, the results seem to be pretty similar to those of its last report (which I discussed in a post last week). The recent report, like last year's report, showed that over the past decade, congestion decreased in five of the nation's largest metropolitan areas: Seattle, Atlanta, San Francisco, Los Angeles, and Detroit). And as I discussed in last week's post, these metro areas have a wide variety of approaches to transportation policy: in San Francisco and Detroit, highway lane-miles per person increased, but in the other three, lane-miles actually increased more slowly than population.

It might be argued that congestion decreased in these cities because economic distress reduced the number of commuters. But in fact, the number of commuters actually increased faster than population in most cities. For example, in San Francisco, population increased by only 2% (from 3.93 million to 4 million) between 2000 and 2009, while the number of commuters increased by over 10% (from 1.71 million to 1.87 million)- more than the increase in the number of lane-miles during this period (from 2335 to 2510, or about 7%). When TTI averaged figures for the fifteen largest urban areas, it came up with a similar result: the average big-region population increased by about 10% (from 5.5 million to 6 million) while the number of commuters increased by about 17% (from 2.34 million to 2.73 million). So if you measure transportation demand by the number of commuters rather than the number of humans, it is even clearer that these regions reduced per-capita highway space.

In sum, it appears that a region can reduce congestion without materially increasing highway capacity.

What happened in the regions that most clearly failed to address congestion? In Chicago, New York, Houston and Philadelphia, hours lost to congestion increased by over 20 percent. In three of these four cities, increases in freeway lane-miles actually outpaced increases in population between 2000 and 2009. In Chicago, population increased by 6% and lane-miles by 13%. In Philadelphia, population increased by 6% and lane-miles by 17% (even more than the i14% ncrease in the number of commuters); in Houston, population increased by 11% and lane-miles by 19% (even more than the 17% increase in commuters). In New York lane-miles increased by slightly less than population. While population increased by 10%, lane-miles increased from 6600 to 7220 (just under 10%).

In sum, the regions that reduced congestion generally did not bother to let road capacity catch up with population growth (let alone the usually higher growth in the number of commuters). By contrast, another group of cities that built roads more rapidly experienced rapid congestion growth instead. This data supports the view that the "road lobby" strategy of widening and building limited-access highways does not relieve congestion.

Michael Lewyn


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