The most effective approach to reducing automobile-related pollution hitherto has been the imposition of emission controls and the associated advances in emissions technology. This explains why today's new vehicles emit only about four percent of the volume of pollutants emitted by cars before emission control mandates⁸ were introduced. It also provides the primary reason why air quality has improved dramatically in Los Angeles and some other California cities since the mid-1970s (in spite of a massive VMT increase). The recurrent tightening of emission controls has created a "moving target" that has stimulated improvements in engine design and emissions equipment.⁹ There is also much more that can be done in this area: continuing the strategy of ever tightening controls, especially to vehicles other than standard cars, e.g. trucks, pickups and SUVs; diffusion of California emission standards nationwide; and, above all, the commercialization of technologies that address the critical "cold start/hot soak" problem. Yet there is widespread agreement that these approaches are not a panacea.¹⁰ The continued increase in VMT implies that a more radical approach is needed, at least in the longer term. I believe that further technical development of gasoline/diesel-electric hybrid vehicles and SULEVs and their significant market penetration offers the best prospects that should bear fruit within the next decade.

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