SUMMARY
When accounting for uncertainty in the data and annualizing the
environmental effects (based on assumed average service lives), the
resource input requirements and the environmental outputs of asphalt
and steel reinforced concrete pavements appear to be roughly comparable.
However, some other environmental burdens have not been
quantified in this assessment. For example, dust emissions, water
usage in manufacturing, nonhazardous solid waste generation and
disposal, generation and disposal of hazardous waste by type, environmental
effects of landfilling, noise and vibration, visual impacts,
and other burdens are currently difficult to quantify because of a lack
of data, and—as in the case of visual impacts—lack of an acceptable
metric. If these other environmental effects had been included, our
assessment might have yielded different conclusions.
During construction, asphalt fumes might pose occupational
exposure hazards to workers in the form of respiratory problems and
eye and throat irritation. (There is no conclusive evidence that they
are carcinogenic.) However, modern paving machines have the
capability to channel fumes away from asphalt workers. In the disposal
phase of the two pavement types, recyclability is demonstrated
for both, but in the United States asphalt pavements have been recycled
in larger quantities than concrete pavements. NAPA reported
in 1997 that asphalt recycling saves over $300 million a year (25).
However, this figure is minuscule compared with the annual expenditure
in the nation for pavement [roughly $39 billion in 1996 (31)].
Based on the LCA performed in this study, asphalt pavements
appear to be an environmentally better choice if they are recycled
effectively. However, uncertainty in the data is large and may have
skewed the results. Also, many other important environmental factors
have not been included in this analysis. Regardless of the environmental
effects, special functional requirements or economics
may dictate the use of one material over the other in particular
applications.