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Transportation Air Quality Facts and Figures January 2006

Traffic Congestion

Percent Change in Urban Congestion


Percent Change in Urban Congestion 1982-2002. Click image for source data.

Congestion occurs when the free flow of traffic on a roadway is impeded due to excess vehicle demand, construction, maintenance, traffic incidents, weather, or other road conditions and events. Many urban areas have experienced increases in traffic congestion in recent years. This map shows the percent change in the amount of extra time per trip it took to travel in the peak period from 1982 to 2002, for selected areas.

Source: Texas Transportation Institute. 2004 Urban Mobility Report. September 2004. Table 5.

Major Sources of Congestion


Pie chart: Major Sources of Congestion 2002. Poor Signal Timing, 5%, Special Events, 5%, Bad Weather, 15%, Work Zones, 10%, Traffic Incidents, 25%, Bottlenecks. 40%

Congestion Mitigation and Air Quality Improvement (CMAQ) program funds can be used for projects and programs that help clear traffic incidents and improve signal timing. Surface Transportation, National Highway System, Bridge, and other federal-aid funds can be used to reduce other sources of congestion, such as bottlenecks and work zones.

Source: Federal Highway Administration. Traffic Congestion and Reliability: Linking Solutions to Problems - Executive Summary. Publication Number: FHWA-HOP-05-004. July 2004.
Web site: 28 June 2005.

Updated: 3/17/2015
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