Vehicle use of roads has steadily increased in the past century. Since the 1960s, urban road travel has become greater than rural road travel; yet the later has more than doubled, and that has important ecological impacts, as discussed in Chapter 3. Indicators of congestion in urban areas are increasing. The extant road system requires large amounts of maintenance and replacement to maintain its current function. Although paved sections of the NHS are considered to be in very good condition for driving, 3 of 10 bridges are structurally deficient or obsolete.
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2 History and Status of the U.S. Road System ."
Assessing and Managing the Ecological Impacts of Paved Roads . Washington, DC: The National Academies Press,
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