The National Highway Traffic Safety Administration (NHTSA) will require automakers to install one of two types of tire pressure monitors on new vehicles beginning November 2003. NHTSA will then undertake a three-year study to determine which system the government will ultimately mandate. The two types are direct tire pressure monitors that determine air pressure and report tire-by-tire results to the driver, and indirect systems that infer tire pressure by using a car’s anti-lock brake system sensors. The new Federal Motor Vehicle Safety Standard applies to passenger cars, trucks, multipurpose passenger vehicles, and buses with a gross vehicle weight rating of 10,000 lbs. or less, except those vehicles with dual wheels on an axle. NHTSA estimates that one in four cars and one in three trucks on U.S. roads are running on at least one substantially under-inflated tire.