June 5, 2002 — The U.S. National Highway Traffic Safety Administration (NHTSA) will allow automakers to install either one of two types of tire pressure monitoring systems that warn motorists when tires are dangerously underinflated, beginning with 2004 model vehicles. One method incorporates MEMS pressure sensors while the other relies on a vehicle’s antilock braking system using wheel speed sensors.

NHTSA announced on May 30 that the U.S. Department of Transportation issued the first of a two-part ruling as part of the Transportation Recall Enhancement, Accountability and Documentation (TREAD) Act of 2000. U.S. lawmakers passed the act after receiving reports of Ford Explorers rolling over, sometimes fatally, when the treads on their underinflated Bridgestone/Firestone tires separated. NHTSA was to determine what constitutes monitoring by the end of November 2001.

The ruling lets automakers choose between systems that monitor tire pressure directly with sensors such as MEMS made by SensoNor, Motorola Inc. and TRW NovaSensor and used by suppliers such as Cycloid Co. and SmarTire Systems Inc. Or they can select a system that infers deflation by measuring and comparing wheel speed rotation. The latter can be incorporated into antilock braking systems, which is considered less expensive but also less precise.

The option will be in effect from Nov. 1, 2003 to Oct. 31, 2006. The transportation department said it will issue a second ruling by March 1, 2005, spelling out performance requirements for the rest of 2006 and later. In the meantime, it will collect studies on the various systems to help it determine those requirements, according to its filing.