Traffic jam

Traffic congestion occurs when the volume of traffic on a roadway is high enough to be detrimental to its performance. In congested conditions, vehicles speeds are reduced increasing drive times. These conditions are also more taxing for drivers, and automobile accidents may be more frequent. Furthermore, vehicles burn unnecessary fuel when stuck at idle. A period of extreme traffic congestion is known as a traffic jam.

Background

In the United States, construction of new highway capacity has not kept pace with population increases and the resulting increase in demand for highway travel. Between 1980 and 1999, road miles of highways increased by only 1.5 percent, while vehicle miles of travel there increased 76 percent.

The Texas Transportation Institute estimates that in 2000 the 75 largest metropolitan areas experienced 3.6 billion vehicle-hours of delay, resulting in 5.7 billion gallons (21.6 billion liters) in wasted fuel and $67.5 billion in lost productivity. Traffic congestion is increasing in major cities, and delays are becoming more frequent in smaller cities and rural areas.

The five areas in the United States with the highest congestion are:

• Los Angeles
• Washington, DC
• Miami-Hialeah
• Chicago
• San Francisco-Oakland

Due to dramatic population increases, San Diego and Las Vegas have seen their congestion levels increase by more than 50 percent since 1982.

Classification

The U.S. Department of Transportation uses the following scale, based on lane occupancy, to classify traffic congestion:

• 35% or higher: Stop and Go
• 22% - 35%: Heavy
• 15% - 22%: Moderate
• 0-15%: Wide Open

Attempts to alleviate traffic congestion

• Road pricing such as the London Congestion Charge, a fee levied on vehicle drivers entering the centre of the city
• Free public transport offered by the local or provincial government, see Public transport#Funding
• Setting of school opening times to avoid problems associated with the school run
• High-occupancy vehicle lanes or "carpool lanes"

See also

• Congestion, for more general usage of the word congestion
• Gridlock
• Journey to work
• Queueing
• Rush hour

External links

• U.S. Department of Transportation (http://www.dot.gov/)
• Science Hobbyist: Traffic Waves (http://www.amasci.com/amateur/traffic/traffic1.html)

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