Shifts between Automobile, Bus, and Bicycle Commuting in an Urban Setting

Abstract

In an urban setting, investments in bicycle and transit modes are expected to reduce automobile vehicle miles traveled. In reality, these benefits might be lower than expected if users simply shift between nonautomobile modes. This article investigates modal shifts among automobile, bus, and bicycle use in students commuting to the University of Wisconsin-Milwaukee (UWM) in 2008 and 2012, when a few changes were made to the local transportation system. The authors found that a significant decline in automobile mode share was associated with a significant increase in bicycle mode share, suggesting that bicycling replaced certain automobile commuting trips. Analysis by distance revealed nuances in mode substitution. There were significant increases in bicycle commuting for students living between 1.6 and 15.9 km (1.0 and 9.9 miles) from campus. However, the increases in bicycling for students living between 1.6 and 3.1 km (1.0 and 1.9 miles) corresponded with decreases in bus rather than automobile commuting, suggesting bus and bicycle substitution for short commutes. There was a significant shift in long-distance commuting—greater than 16 km (10 miles)—from automobile to bus. The authors also analyzed primary and secondary travel modes and found an increase in the proportion of regular automobile commuters who bicycled as their secondary mode. Moreover, approximately two-thirds of the students whose primary mode was bicycle and nearly half of the students whose primary mode was bus used a different, secondary commute mode. These results suggest the importance of investigating secondary travel modes.