Traffic congestion is the level at which transportation system performance is no longer acceptable due to traffic interference. High lane occupancy percentages indicate congested conditions. The U.S. Department of Transportation uses the following scale to define traffic congestion based on lane occupancy:
- 35% or higher: Stop and Go
- 22% - 35%: Heavy
- 15% - 22%: Moderate
- 0-15%: Wide Open
The Texas Transportation Institute estimates that, in 2000, the 75 largest metropolitan areas experienced 3.6 billion vehicle-hours of delay, resulting in 21.6 billion liters (5.7 billion gallons) in wasted fuel and $67.5 billion in lost productivity. And traffic volumes are projected to continue to grow. Typically, traffic congestion is viewed as a big city problem, but delays are becoming growingly common in smaller cities and even in rural areas.
The five areas showing the highest congestion levels were: Los Angeles (1.57), Washington, DC (1.43), Miami-Hialeah (1.34), Chicago (1.34) and San Francisco-Oakland (1.33). Cities with the lowest congestion levels were: Bakersfield, California (0.68), Laredo, Texas (0.73), Colorado Springs, Colorado (0.74), Beaumont, Texas (0.76), and Corpus Christi, Texas (0.78). While San Diego and Las Vegas saw their congestion levels increase by more than 50 percent since 1982, conditions worsened at the same rate in three smaller cities: Salt Lake City, Utah, Albany-Schenectady-Troy, N.Y., and Eugene-Springfield, Ore.
Attempt to alleviate traffic congestion include:
- road pricing, such as in London the London Congestion Charge, a fee levied on vehicle drivers entering the centre of the city
- free public transport, sometimes offered by the (local, provincial) government, see Public transport#Funding.
- Congestion, for more general usage of the word congestion