Can't Build Our Way Out?
Houston and Phoenix Deflate a Popular Myth
By Wendell Cox and Alan Pisarski

Traffic congestion cannot be reduced by building additional roadway capacity is a popular view. This theory holds that new roadways create or induce additional travel demand and that, as a result, there is no point to building more roadway capacity, since new roads cannot reduce traffic congestion.

This is not a convincing argument to residents of the Houston area, who significantly reduced traffic congestion by building new roadway capacity. As late as 1985, Houston had the worst traffic congestion in the United States. In response Houston took steps, particularly under Texas Department of Transportation Chairman and then Mayor Robert Lanier, to expand urban roadway capacity, both freeways and non-freeway arterials. Houston’s experience has demonstrated that sufficient capacity can be built to serve the demand. By 1993, traffic congestion-related delays had declined 40 percent. In more recent years, the Lanier policies have not been continued, but traffic congestion remains below the 1986 peak and similar to far smaller Portland (which had less than one-fifth Houston’s traffic intensity in 1986).

Further, average roadway travel per capita increased only 10 percent in Houston from 1984 to 2002, less than one-third the national rate. If new roadway capacity routinely “induced” additional travel, then per capita driving should have increased in Houston compared to the rest of the nation.

The emptiness of this “induced traffic” theory is further demonstrated by the experience of Phoenix. In the middle 1980s, Phoenix had a severely underdeveloped freeway system compared to other major urban areas in the United States. At that time, Phoenix undertook construction of new freeways. Phoenix has built more new urban freeways than any other major urban area in the last two decades.

Based upon the induced traffic theory, residents of the Phoenix area should have rushed out to drive even more, and overall travel volumes should have increased inordinately compared to other areas. In fact, the opposite occurred. Overall travel volumes in the Phoenix area increased 20 percent per capita from 1984 to 2002. This is well below the national urban average increase of 32 percent. Perhaps even more significantly, Portland, with its adopted anti-freeway policies, experienced a 52 percent per capita increase in car use over the same period.

In fact, where metropolitan roadways have been substantially improved, virtually no “induced traffic” effect has been noted. Of course new roads do attract new traffic. However, they attract traffic from other roads more than they “induce” it. What appears to some to be “induced” demand may be nothing more than pent-up demand for better roadways. FHWA research indicates that, even where a small, induced demand factor can be identified, it largely disappears when considered in terms of driving time (vehicle hours) instead of distance (vehicle miles).

Wendell Cox is principal of Wendell Cox Consultancy and a visiting professor at the Conservatoire National des Arts et Metiers in Paris. Alan Pisarski is a transportation consultant and author of the popular book series, Commuting in America. This piece was excerpted from a forthcoming Reason Foundation study.

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