With few exceptions, a revised U.S. regulation on braking requires that new heavy-truck tractors be able to stop in 250 ft when loaded to their gross vehicle weight rating (GVWR) and tested at 60 mph. That is 30% shorter than currently required under Federal Motor Vehicle Safety Standard 121. Compliance dates are Aug. 1, 2011, for three-axle tractors with a GVWR of 59,600 lb or less, and Aug. 1, 2013, for two-axle tractors and tractors with a GVWR above 59,600 lb. For a small number of very-heavy, severe-service tractors, the stopping distance will be 310 ft under the same conditions. All tractors must stop within 235 ft when loaded to their "lightly loaded vehicle weight." The stopping-distance requirements were published by NHTSA (National Highway Traffic Safety Administration) on July 27. The agency expects the rule to save 227 lives annually and prevent 300 serious injuries.