More than 20 countries, including the United States, France and Britain, have agreed to require safer sliding doors on minivans as the first international safety standard for motorized vehicles, the United Nations said Thursday. The new regulation strengthens safety requirements and test procedures for sliding doors used on many passenger vehicles, which should help to prevent injuries and deaths by keeping passengers inside the vehicle when there is an accident, the U.N. Economic Commission for Europe said. "Today in Geneva we have witnessed a new milestone toward the improvement of road traffic safety throughout the world," said Jose Capel Ferrer, UNECE transport chief. "We are optimistic that this will be the first in a long series of such global regulations, which will also improve the environmental performance of vehicles at the global level." Doors are often forced open by a combination of forces when a vehicle crashes, resulting in structural failures in latch systems and hinges. This happens about 42,000 times every year in the United States alone, presenting "a serious risk of injury or death to vehicle occupants, particularly if they are unbelted," UNECE said. More standards are being considered, including for head restraints, motorcycle brakes and pedestrian safety, the agency said. Eventually, reduced design and engineering costs should lower production costs and customer prices.