MTR 111, Feds Say They May Consider Induced Traffic

Mobilizing the Region
Issue 111 January 17, 1997

Feds Say They May Consider Induced Traffic

Compelling evidence that highway expansion creates new traffic is slowly creating a professional consensus around the fact of "induced travel demand." Still, considerable disagreement remains over the extent of the phenomenon, and over what should be done about it. Kevin Heanue, the Federal Highway Administration's director of environment and planning, indicated at a panel on capacity expansion and induced travel at the annual meeting of the Transportation Research Board in Washington, DC. Tuesday that an FHWA study of Milwaukee found that traffic created by new highway capacity between 1960 and 1990 can be held responsible for wiping out 8-22% of the time savings the new capacity had afforded.

But earlier, professor Mark Hansen of the University of California summarized his studies of past highway expansion and traffic growth in California, which indicating that each 10% increase in highway lane-miles has induced an immediate 2% increase in traffic at the county level, building to a 6% increase within two years. When induced traffic in neighboring counties was counted, Hansen found that traffic growth was even greater at the metropolitan level -- 9% for each 10% increase in capacity. Thus, highway-building in California has brought only modest relief to congested corridors and has largely worsened rather than eased regional gridlock.

The prestigious U.K. Standing Committee on Trunk Road Assessment reached a similar conclusion in its 1995 report on traffic generation.

Encouragingly, in response to a question from Michael Replogle of the Environmental Defense Fund about FHWA's modeling guidelines on peak spreading, time of day for travel, and other key parameters involving induced traffic, Heanue said "Our guidelines have reflected the consensus. As that changes, we'll change them." Presently, the "build/no-build" test used for highway environmental impact statements admits no induced travel effects. Changing this, and the way Clean Air Act clean air/transportation "conformity" rules treat the question, could begin to tip the legal scales more firmly in favor of projects that offer real alternatives to driving, rather than more traffic down the road. Advocacy groups in Washington are seeking further discussion with FHWA on the issue.

(Hansen's study is summarized in the Fall 1995 Access, U.Calif. Transportation Center, 510-643-5454, access@uclink.berkeley.edu. See also MTR #61.)