Measuring Traffic Reduction from Bicycle Commuting

Abstract

Increased bicycle commuting is said to reduce motor vehicle traffic, but can this reduction be measured? To address one aspect of this question, Bike to Work Day events are used to explore how the volume of motor vehicle traffic changes when the volume of bicycle traffic doubles. In many communities, Bike to Work Day is an annual 1-day event that encourages commuting by bicycle. Because event participation rates were high in Boulder, Colorado, the city was chosen as an example to investigate this issue. Bicycle and motor vehicle traffic volumes measured by continuous counters on Bike to Work Day were compared with volumes from comparable workdays. Bicycle volume on Bike to Work Day was roughly double that on comparable workdays; motor vehicle volume on Bike to Work Day was lower than on comparable Wednesdays in 88% of the 16 cases studied and significantly lower at the 80% confidence level in 31% of the cases. The observed decrease in motor vehicle volume is of the order of magnitude expected for the observed increase in bicycle volume. Results of a one-tailed t-test for paired samples indicate that the decreased traffic counts on Bike to Work Day are significant at the 95% confidence level versus counts on other summer Wednesdays. These results suggest that bicycling can be a practical alternative to commuting by motor vehicle for some people and demonstrate that corresponding decreases in the volume of motor vehicle traffic can be measured.