U.S. Department of Energy - Energy Efficiency and Renewable Energy
Vehicle Technologies Program
Fact #472: June 4, 2007
The Causes of Traffic Congestion
Bottlenecks, or capacity problems, have been identified as the major cause of traffic congestion. Forty percent of urban road traffic congestion is caused by bottlenecks. Another 25% of congestion is caused by traffic incidents, such as crashes and disabled vehicles. Other causes for congestion include bad weather, work zones, poor signal timing, and special events/other reasons.
Causes of Traffic Congestion 
Supporting Information
Causes of Traffic Congestion
| Bottlenecks |
40% |
| Traffic Incidents |
25% |
| Bad Weather |
15% |
| Work Zones |
10% |
| Poor Signal Timing |
5% |
| Special Events/Other |
5% |
|
Source: Congressional Research Service, Surface Transportation Congestion: Policy and Issues, May 10, 2007. (Original source: Cambridge Systematic and Texas Transportation Institute.) |
Return to 2007 Facts of the Week
|