WASHINGTON, D.C. – Cars are becoming safer, but the people who drive them are not, an Insurance Institute for Highway Safety study found. In fact, without design changes that have made vehicles safer, including the growing prevalence of airbags, the death toll on the nation’s roads would be higher by about 5,000 people annually, more than 11 percent of last year’s total, primarily because drunken driving rates have not changed much in the 10 years studied, seatbelt use has climbed at only a moderate pace, and people are driving faster. According to a preliminary estimate by the government’s National Highway Traffic Safety Administration, the death rate per million miles traveled has fallen almost every year since 1966, although it was up slightly in 2005. It would have risen in the 10 years ended 2004, rather than falling 16.8 percent, if not for the improvements in vehicles, the insurance institute’s study found. “Every year we look at the fatality rate and it is coming down, and people are becoming complacent; people think we’re doing everything right,” said Adrian Lund, an author of the study, which examined the period from 1994 to 2004, as quoted in the New York Times. “Our results show in recent years it’s only because we’re doing such a good job of getting people into safer vehicles.” Belt use among front-seat occupants increased to about 80 percent in 2004, from about 58 percent in 1994, and is about 82 percent now. The agency says each increase of one percentage point in belt use saves some 270 lives a year; highway deaths last year were about 43,200. The study also noted that increased vehicle safety during the decade correlated with an increase in average vehicle weight and size, a trend that is unlikely to survive in an era of $3-a-gallon gasoline.