table of contents - Research and Innovative Technology ...

ed? In what complex areas of environmental
damage is our information and knowledge
inadequate to form a reliable opinion?
� Metropolitan air quality. What progress is
being made in improving metropolitan air
quality where 90 million of the 200 million
residents were estimated to be exposed to
unhealthy levels of air pollution during some
period in 1994? As we go beyond technologybased
solutions to reduce emissions, what is
the promise of the various short- and longterm
transportation control measures (TCMs)?
� International comparisons. How does transportation-related
air quality in the United
States compare with that in other industrialized
countries and in the newly industrializing
developing countries? As developing
countries are on the threshold of a rapid
motorization phase, how will air quality and
greenhouse gas emissions be affected and
what are the climate change implications?
Environmental Impacts of Transportation
Transportation-related activities can degrade
environmental quality and adversely impact
human health and productivity. Motor vehicle
emissions are a significant source of urban air
quality problems. Carbon dioxide emissions
from the combustion of fossil fuels by vehicles
are increasing the concentration of greenhouse
gases, which have the potential to alter the
earth’s climate. Crude oil and gasoline leaks and
spills from tankers, motor vehicles, and aboveand
below-ground fuel storage tanks pollute surface
and groundwater. Old vehicles, tires, and
paving materials that are not recycled can cause
problems for landfills, contaminate water systems,
and contribute to air pollution emissions.
Transportation infrastructure affects land use,
flora and fauna habitats, and may cause changes
in local water tables and drainage patterns.
The extent of these environmental impacts
depends on the complex interactions of trans-
portation-related pollution with local geographic
and meteorological conditions, technology,
markets, and public policy. Although governments
play important roles in supplying components
of transportation infrastructure and in
carrying out environmental policies pertaining
to transportation, the vast majority of transportation
decisions are made in the marketplace
by businesses and individuals.
Markets are efficient at producing and allocating
private goods and services, but they tend
to ignore the environmental harm that can occur
from the byproducts of transportation activities.
Pricing mechanisms seldom reflect environmental
damage in the cost of transportation, and this
has been a rationale for government intervention
through environmental policies and standards.
Emissions standards for newly manufactured
highway vehicles first imposed by the federal
government in the late 1960s and early 1970s
are examples. Today, more than 20 laws have
provisions that address many environmental
impacts from transportation. The effectiveness
of these laws is somewhat dependent on the
accuracy and comprehensiveness of data on
environmental impacts. Over the past 25 years,
a good deal of progress in data collection has
been made, particularly for motor vehicle
emissions. Unfortunately, other aspects of
environmental quality are less well documented.
More needs to be known about transportation
impacts on surface and groundwater
resources and the interaction between transportation
and land use, particularly in terms of
the costs of urban sprawl.
Much of the data about the environmental
impacts of transportation was developed to
monitor progress in meeting the goals of national
policies. Hence, there are many limitations to
the data. For the most part, the environmental
management system now in place treats each
kind of pollution separately, even though there
are complex interactions among environmental
media. Most analyses of transportation’s envi-
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