page_title: Megacity
section_title: Traffic congestion
hierarchical_section_title: Megacity / Challenges / Traffic congestion
caption_attribution_description: English: Traffic jam in Bangkok, Thailand.
context_page_description: A megacity is a very large city, typically with a population of more than 10 million people. Precise definitions vary: the United Nations Department of Economic and Social Affairs in its 2018 "World Urbanization Prospects" report counted urban agglomerations having over 10 million inhabitants. A University of Bonn report held that they are "usually defined as metropolitan areas with a total population of 10 million or more people". Others list cities satisfying criteria of either 5 or 8 million and also have a population density of 2,000 per square kilometre. The terms conurbation, metropolis, and metroplex are also applied to the latter.
  The total number of megacities in the world varies between different sources: The world had 33 according to the UN, 37 according to CityPopulation.de, and 35 according to Demographia. Many of these urban agglomerations are in China and India. The other four countries with multiple megacities are the United States, Brazil, Pakistan, and Japan.
context_section_description: Traffic congestion is a condition on road networks that occurs as use increases, and is characterized by slower speeds, longer trip times, increased pollution, and increased vehicular queueing. The Texas Transportation Institute estimated that, in 2000, the 75 largest metropolitan areas experienced 3.6 billion vehicle-hours of delay, resulting in 5.7 billion U.S. gallons (21.6 billion liters) in wasted fuel and $67.5 billion in lost productivity, or about 0.7% of the nation's GDP. It also estimated that the annual cost of congestion for each driver was approximately $1,000 in very large cities and $200 in small cities. Traffic congestion is increasing in major cities and delays are becoming more frequent in smaller cities and rural areas.
caption: Bangkok is notorious for its traffic congestion.
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