The recession and high gas prices have helped a bit by reducing the number of miles traveled, and perhaps cutting average speed, at least for part of the period. But that is a small part of the improvement. Measured by deaths per miles traveled, a yardstick that filters out the effect of less driving, the death rate is down by 16.1 percent from 2005 to the first half of 2009.

Improvements in automotive safety are dramatic. One could argue the ‘Cash for Clunkers’ even contributed to these improvements as older cars were replaced with newer models with safety improvements. What else caused the drop?

Government officials and private experts cite a variety of factors. Highways are built or renovated with more consideration for safety. Seat belt use rose over the period, although some experts are skeptical about the accuracy of official counts. As old vehicles are retired, the ones that replace them have more air bags, antilock brakes and stability control systems, which sense when a car is in a skid and apply a brake to one wheel to help the driver regain control. In addition, new restrictions are in place for licenses for teenagers.