ciety of Automotive Engineers (SAE). In particular, the SAE Progress in Technology (Johnson 2002a,b; Johnson 2005a,b) series contains collections of SAE technical papers relating to specific technologies, including combustion and pollutant control in internal combustion engines. The Manufacturers of Emissions Control Association ( is another source for more comprehensive information on mobile-source emissions controls.


A central concept of the standards-setting process for mobile-source emissions by EPA and CARB is “technology forcing.” The committee defines a technology forcing standard to be the establishment by a regulatory agency of a requirement to achieve an emissions limit, within a specified time frame, that can be reached through use of unspecified technology or technologies that have not yet been developed for widespread commercial applications and have been shown to be feasible on an experimental or pilot-demonstration basis. The use of technology-forcing standards in the United States contrasts with the standards-setting process in Europe where new emissions-control technologies on mobile sources are required only after they have succeeded in the U.S. market (Faiz et al. 1996).

When controls on vehicle emissions were first considered in Los Angeles in the 1950s, requiring of devices that were not commercially available was not accepted as a viable approach. Los Angeles County Supervisor Kenneth Hahn was denied permission to require the installation of emissions-control devices on vehicles sold in the county by a county legal counsel opinion that stated, “Any such requirement would be “arbitrary, capricious, and void” until “a satisfactory device is perfected and available on the market” (Krier and Ursin 1977, p. 98, as cited in Lents et al. 2000, p. II-10). Lack of progress on air pollution control in California and elsewhere in the United States prompted Congress in the 1970 CAA amendments to feature ambient air quality standards with deadlines for their attainment and a technology-forcing program to reduce emissions from vehicles (Muskie 1990). Chief Senate sponsor, Senator Edmund Muskie, stated that the CAA was not “to be limited by what is or appears to be technologically or economically feasible” but “to establish what the public interest requires to protect the public health of persons” even if that means that “industries will be asked to do what

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