How the Reconstruction of I-880 Affected Travel Behavior

One of the concerns that people have about expanding highway capacity is that this will motivate more people to travel, so that the highway will soon become as congested as before. This is also a concern with automated vehicles, which would have the effect of increasing capacity. This so-called induced travel has been a subject of much debate and study in recent years. One of the problems confounding studies of this subject has been that capacity increases are generally motivated by recent or expected development, which generates increased travel and can even increase per capita travel if it increases the size or general prosperity of the metropolitan area. The reopening in 1999 of the section of I-880 that was destroyed by a 1989 earthquake in the San Francisco Bay area provided a unique opportunity to study the effects of a significant highway capacity expansion that was not motivated by development. Because it was out of service for 10 years, people had ample time to adjust their travel patterns to its absence so that its reconstruction represented an increase in capacity rather than the restoration of temporarily diminished capacity. This study utilized traveler questionnaires to determine how the reduced travel time afforded by reconstruction had affected travel patterns. The paper begins with a discussion of the mechanisms by which increased highway capacity affects travel, followed by a review of the literature on induced travel. Then the survey methodology is described, the results presented, and conclusions drawn.