Traffic fatalities on the nation's roads are down nearly 10% over last year and the number of people killed in crashes this year is expected to reach the lowest level. The lower fatality levels come at a time when Americans have significantly reduced the amount they drive. Chandra Bhat, a professor of transportation engineering at The University of Texas who studies driver behavior, said that fewer miles driven means fewer wrecks. "Researchers must first determine who is driving less because fatalities generally are higher among teen and elderly drivers," he said. Another factor to consider is what time of day the reduction in driving is occurring because nighttime crashes generally are more fatal than daytime wrecks.