Source: Texas Transportation Institute. The 2005 Annual Mobility Report.
Traffic Conditions in Major American Cities, 1982-2003
While in the early 1980s, the great majority (65%) of urban circulation
in major American cities occurred in an uncongested setting, by the
early 21st century the situation degraded considerably. About 66% of
the urban circulation occurs under congestion and more than half of
it under heavily congested situations. Major factors linked with this
situation are related to urban sprawl, a growing fleet of trucks and
automobiles and the difficulty to provide additional road infrastructures.