Michael Sivak for the University of Michigan Transportation Research Institute

This study found that a 2.7% decline in vehicle travel caused by fuel price increases and a weak economy during 2007-08 resulted in much larger 17.9% to 22.1% month-to-month declines in traffic deaths, probably due to disproportionate reductions in vehicle travel by lower income drivers (who tend to be young and old, and therefore higher than average risk), and speed reductions to save fuel.