NHTSA (U.S. National Highway Traffic Safety Administration) on May 16 proposed a rule to require that new large commercial truck tractors and buses be equipped with an electronic stability control (ESC) system. If and when the proposed rule is adopted, the mandate would take effect two years later for all new typical 6 x 4 truck tractors and four years for severe-service tractors and tractors with four or more axles. In justifying the lead times, NHTSA noted that there are only two suppliers of ESC systems for truck tractors and large buses: Bendix and WABCO. It said the current rate of ESC installation on new truck tractors is 18%.