Background: Motor vehicle drivers make decisions about speed while traveling and thereby trade off a potential saving from shorter travel time (if the trip is uneventful) against a potential loss of time (if the trip results in a crash).
Methods: The authors used computerized modeling based on national data to examine the benefits from small changes in average driver speed on public health in the United States. Lost time due to both travel and crashing was calculated, along with optimal speed to minimize net time lost.
Results: The baseline analysis suggested that 1 hour spent driving was associated with approximately 20 minutes of additional lost time in life expectancy due to the potential of a crash. A approximately 1-km/h (0.6-mph) increase in speed for the average driver yielded a approximately 26-second approximate increase (not decrease) in total expected lost time because the savings from reduced travel time were more than offset by the increased prospect of a crash. A 3.0-km/h (1.8-mph) decrease in average driving speed yielded the least amount of total time lost (95% confidence interval [CI]: 2.5-4.1 km/ h [1.5-2.5 mph]). This speed yielded about 11,000 fewer crashes each day, saved about 3.6 hours per year for the average driver (95% CI: 2.0-6.2 hours), and conserved about 199 cumulative life years for society annually.
Conclusions: As a nation, drivers in the United States travel slightly too fast and could improve overall life expectancy by decreasing their average speed slightly.