In setting limits on vehicle emissions, it is important to
distinguish between
technology-forcing
and
technologyfollowing
emission standards. Technology-forcing standards
are at a level that, though technologically feasible,
has not yet been demonstrated in practice. Manufacturers
must research, develop, and commercialize new technologies
to meet these standards. Technology-following
standards involve emission levels that can be met with
demonstrated technology. The technical and financial
risks involved in meeting technology-following standards
are therefore much lower than those of technology-forcing
standards. In the absence of effective market incentives
to reduce pollution, vehicle manufacturers have
little incentive to pursue reductions in pollutant emissions
on their own. For this reason, technology-forcing
emission standards have provided the impetus for nearly
all the technological advances in the field.