Car manufacturers are doing a better job designing sport-utility vehicles to resist rollover accidents, according to news reports this week. The National Highway Traffic Safety Administration said that 24 SUVs earned four-star rollover ratings in tests conducted during the 2005 model year. Four years ago, when the government first issued rollover ratings, just one SUV got four stars: the Pontiac Aztek. NHTSA chief Jeffrey Runge said one of the keys has been the development of crossover vehicles, which have lower centers of gravity. But he conceded that because of the relatively slow turnover in the nation's vehicle fleet, it will be years before the improved ratings translate into significantly fewer rollover deaths.Rollover fatalities account for 25 percent of the 43,000 highway fatalities each year. Cars continue to get the best rollover ratings, followed by minivans. SUVs on average are improving. Pickups have improved less, NHTSA says. The Ford Freestyle 4x4 was rated the best among the four-star vehicles, with a 13 percent chance of rollover.