In a 1995 Access article, Mark Hansen drew upon 18 years of data to show that, in California metropolitan areas, every 10 percent increase in road capacity brings about a nine percent increase in traffic volumes within just a few years. The article was used by environmental groups as evidence that new roads don't solve congestion problems. The author draws a different conclusion. In this article, the author argues that road supply and demand are continually influencing each other, but most studies emphasize only the demand aspect. Traffic will increase not just on any new road, but on new roads that offer a specific benefit, such as increased speed. In addition, previous studies have failed to examine the link between road expansion and land development. In the past, researchers have focused on behavior shifts-the way driving patterns have changed as new roads are added- but the author argues that this is only part of the story. In addition to short-term behavioral changes, there are long-term structural changes that must be considered. For instance, new roads that allow for faster speeds lure in developers. As homes and businesses go up alongside these roads, even more travelers are drawn to them.
Abstract