Abstract
The causal link between driver cell phone use and crash rates was investigate by exploiting a natural experiment induced by the 9 PM price discontinuity that characterizes a majority of recent cellular plans. First a 7.2 percent jump was documented in driver call likelihood at the 9 PM threshold. Using a prior period as a comparison, next no corresponding change was documented in the relative crash rate. These estimates imply an upper bound in the crash risk odds ratio of 3.0, which rejects the 4.3 asserted by Redelmeier and Tibshirani (1997). Additional panel analyses of cell phone ownership and cellular bans confirm these result. (Author/publisher)