The full text of this working paper is available as an Adobe Acrobat PDF.

Summary

Cell phone use is increasing worldwide, leading to a concern that cell phone use while driving increases accidents. Several countries, as well as two states and many municipalities in the U.S., have banned the use of hand-held cell phones while driving. In this paper, we develop a new approach for estimating the relationship between cell phones use while driving and accidents. Our approach is the first to allow for the direct estimation of the impact of a cell phone ban while driving. It is based on new survey data from over 7,000 individuals.

This paper differs from previous research in two significant ways: First, we use a larger sample of individual-level data; and second, we test for selection effects, such as whether drivers who use cell phones are inherently less safe drivers, even when not on the phone.

The paper has three key findings. First, there is evidence of selection effects. Our analysis suggests that individuals who are more likely to use hands-free devices are more careful drivers even without them. Once we correct for the endogeneity of hands-free usage, our models predict no statistically significant reduction in accidents from mandating that usage must be hands-free. Second, we find that the impact of minutes of cell phone use on accidents varies across the population. Even after controlling for observed driver characteristics, our random coefficient models show there is additional variation in the cell phone impacts on accidents, particularly for female drivers. Previous studies of cell phone usage and accident risk are thus subject to selection bias. We calculate that previous estimates of the impact of cell phone usage on risk for the population may be overstated by 36%. Finally, we explore the impact of a ban on cell phone use while driving. We cannot reject the hypothesis that a ban would have no effect on the number of accidents. Our estimates of the reduction in accidents from a ban on cell phone use while driving are both lower and less certain than previous studies indicate.