Reasons for Recent Large Increases in Commute Durations

This paper describes a study of daily personal travel time in the Minneapolis-St.Paul, Minnesota metropolitan area and how and why it changed between 1990 and 2001.This has two major components. The first is the relationship between commute and non-commute travel time. The second is the relationship between mode choice, total dailytravel time, and automobile travel time. Both of these are analyzed in terms of how theyvary geographically within the region as well as how they changed during the decade. The study is based on the Twin Cities Travel Behavior Inventory (TBI), whichincluded about 10,000 households in 1990 and about 5,000 in 2001. These large samplesmake it possible to study geographic variations within the region. This is supplementedwith information on commute durations from the Census Transportation PlanningPackage. Average Twin Cities one-way commute durations increased by about two minutesduring the 1990s, while total daily travel time increased by about five minutes forworkers and two minutes for non-workers. This supports an earlier finding that variationsin total daily travel time within the region were primarily due to differences in averagecommute durations rather than non-work travel. The findings here also support the theorythat time spent in non-auto modes reduces the amount of time spent in auto travel,although the reduction is not one-for-one.