September 28, 2003

RALEIGH — Contrary to the belief of many city planners and public officials in North Carolina, highway projects do not play a large role in determining the amount and nature of growth in local communities, according to a new study from a nationally renowned transportation scholar.

Dr. David Hartgen, a professor of transportation studies at the University of North Carolina at Charlotte and a John Locke Foundation policy analyst, conducted a new study for JLF that compared the location of major highway projects in North Carolina during the 1990s and the amount of population growth in and around those areas.

He found only a “modest” relationship — so modest, in fact, that factors such as geography, zoning, taxes, schools, the availability of water and sewer service, the presence of retail, and the preexisting density played a much more significant role in determining the rate of growth during the decade.

“Road projects are blunt and inefficient instruments for either spurring or slowing growth,” wrote Hartgen, a former planner and policy analyst for the New York State Department of Transportation and the Federal Highway Administration. “The analysis also showed that about half of the population growth in North Carolina in the 1990s went into tracts that had no major road improvements during the decade.”

Several implications followed from this finding, he said. Many local communities expecting large economic benefits from state road projects, especially those in rural areas of North Carolina, are likely to be disappointed by the relatively modest potential impact, he said. In fast-growing regions, on the other hand, advocates of “Smart Growth” policies will likely be disappointed if they seek to use highway policy to determine growth patterns rather than, as Hartgen suggested, simply to address traffic congestion and safety concerns.

“Officials should cautiously consider proposed changes in road funding policy that offer hope of slowing or stopping sprawl or growth since such policies are likely to be unsuccessful,” he said. As long as a community is an attractive place to live and generates employment opportunities, growth will probably follow — so a failure to build roads to accommodate the resulting traffic will only result in more congestion, he said.

“Induced traffic” from highway projects

On a related point, Hartgen questioned the logic of those who suggested that improving highway capacity will fail to alleviate congestion because it will only create more sprawling development and, thus, more traffic. The “induced capacity” effect of highway expansion — the number of new drivers added from growth — is only a small percentage of the daily traffic the highway expansion accommodates, he said, while urban areas across the United States that have failed to build enough highway capacity are precisely those with some of the worst traffic congestion.

“Even a very large road improvement would have much less effect on traffic generation . . . than a modest commercial strip with just five or six restaurants or stores,” he wrote. “Since the capacity expansion of a typical two- to four-lane road widening is in the range of 20,000 trips per day, the effect of the widening itself is small relative to the carrying capacity of the expansion.”

While some public officials and policy analysts have blamed low-density development patterns in North Carolina and the United States on the construction of the interstate highway system during the second half of the 20th century, Hartgen’s model found that proximity to interstates did not generally correlate with subsequent growth. Rising incomes, the desire of families to own larger homes on larger lots, and other factors drove residential development into suburbs and beyond, and helped create lower-density neighborhoods within metropolitan areas.

“It is largely coincidental, not causal, that the interstate system, when laid on top of this pattern, shows apparent spatial correlation with growth or lower density,” he wrote.

Which is best: building or widening?

In addition to his findings about the effects of road projects on growth and sprawl, Hartgen was also able to assess the relative cost-effectiveness of alternative uses of highway dollars across North Carolina such as building new roadways, adding lanes, or adding new exits. Assessing the projects based on how much traffic they served in the area and how much the change cost, Hartgen concluded that widening major highways, particularly in urban areas, had been the most cost-effective investment, while widenings and new roads in rural areas were far less cost-effective. Adding new exit ramps was the least-efficient use of highway dollars, he found.

“More study is needed to determine why these projects vary so much in cost-effectiveness and how the state can improve the delivery of more cost-effective projects,” Hartgen wrote.

Please call JLF Vice President for Research Roy Cordato at 919-828-3876 for more information on the new highway study. The full report, an executive summary, and a PowerPoint presentation of the results can be found online.