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Page 19

Air Pollution and Mobility

Air pollution is the justification for spending automo-

tive gas taxes on transit and other non-road-related proj-

ects.  ISTEA, which has clear links to the Clean Air Act

Amendments of 1990, particularly limits how cities that do

not meet clean air standards can spend their share of feder-

al transportation dollars.

Automobiles produce several significant pollutants,

including carbon monoxide (CO), nitrogen oxides (NOx),

hydrocarbons (HC), particulate matter, and volatile organic

compounds (VOCs).  Between 1971 and 1996 federal air pollu-

tion requirements reduced most emissions from new cars by 80

percent to 95 percent.34

That reduction has significantly improved the air

quality of most American cities.  Except for Los Angeles,

virtually every city that was out of compliance with federal

air quality standards (the "pollution standards index") on

more than one day in 1983 saw at least a two-thirds reduc-

tion in the number of days it violated those standards by

1992.35

At the same time, Americans are driving more than ever.

Due partly to the increasing number of women in the work-

force and partly to a growing economy, the number of miles

driven per person is increasing by more than 2 percent per

year.36  That suggests that urban air pollution might worsen

again in the future.

When Congress imposed air pollution standards on new

cars, it made no changes to the standards for older cars.  A

California study found that half of all automotive air

pollution comes from the dirtiest 10 percent of all cars--

mostly older cars.37  Removing those dirty cars from the

road would do more to clean up the air than would imposing

tighter standards on new cars.

What Pollutes

For any given car, most pollution is a function of

three variables:

· Engine temperature: HC and, to a lesser extent, CO

are mostly produced when a vehicle's catalytic convert-

er is not yet heated to operating temperature.  Thus, a

cold start followed by a 2-mile trip produces almost as

much HC and CO as a cold start followed by a 10-mile