CONTROL OF MOTOR-VEHICLE EMISSIONS - THE UNITED-STATES EXPERIENCE

An historical overview of U.S. experience with highway motor vehicle emissions control is presented. The evolution of new motor vehicle emissions certification practice, end-of-assembly-line inspection, in-use surveillance and recall, inspection and maintenance, and antitampering programs is discussed. The changes in motor vehicle design and fuel formulation resulting from these practices are also described, along with associated changes in the characteristics of emissions. Although significant reductions of new motor vehicle emission rates have been experienced, excessive consumer tampering and poor maintenance, along with large increases in the number of roadway miles traveled, have decreased the magnitude of air quality improvements resulting from these control efforts. As a result of these and other observations, the U.S. Congress amended the Clean Air Act in 1990 to require more stringent new motor vehicle emission standards, changes in procedures for identification and repair of motor vehicles that have been tampered with or poorly maintained, and use of cleaner, more environmentally benign alternatives to conventional petroleum-based fuels.