Car accidents, smartphone adoption and 3G coverage

This paper examines the relationship between smartphone use by drivers and traffic accidents in California between 2001 and 2013. To estimate smartphone use, the authors first identify when the widespread adoption of modern smartphones began in 2009 following the release of the iPhone 3G and T-Mobile G1.

Smartphone use estimates are combined with annual 3G coverage maps constructed from cellular tower information using a machine learning framework. Using a difference-in-differences design, the authors estimate the combined effect of smartphone adoption and 3G coverage on quarter-mile road segments.

Controlling for census tract population density, road and year fixed effects, Poisson regression results show a statistically significant increase in traffic accident rates along road segments where smartphone use becomes possible. The preferred specification indicates that smartphones increase accident rates by 2.9%, resulting in approximately 3,500 additional accidents per year in California.

Robustness checks and comparisons with individual-level studies support the findings. The results guide policies aimed at reducing distracted driving and cell phone–related accidents.