page_title: Traffic bottleneck
section_title: Dynamic bottleneck
hierarchical_section_title: Traffic bottleneck / Graphical and theoretical representation / Dynamic bottleneck
caption_attribution_description: English: Tractor on the road. Picture taken at Cacouna, Québec, Canada, 12th of June 2005.
context_page_description: A traffic bottleneck is a localized disruption of vehicular traffic on a street, road, or highway. As opposed to a traffic jam, a bottleneck is a result of a specific physical condition, often the design of the road, badly timed traffic lights, or sharp curves. They can also be caused by temporary situations, such as vehicular accidents.
  Bottlenecks can also occur in other methods of transportation. Capacity bottlenecks are the most vulnerable points in a network and are very often the subject of offensive or defensive military actions. Capacity bottlenecks of strategic importance - such as the Panama Canal where traffic is limited by the infrastructure - are normally referred to as choke points; capacity bottlenecks of tactical value are referred to as mobility corridors.
context_section_description: For this example, consider three lanes of traffic in one direction.  Assume that a truck starts traveling at speed v, more slowly than at the free-flow speed vf.  As shown on the fundamental diagram below, speed qᵤ represents the reduced capacity (two-thirds of Q, i.e., 2 out of 3 lanes available) around the truck.
  State A represents normal approaching traffic flow, again at speed vf. State U, with  flowrate qᵤ, corresponds to the queuing upstream of the truck. On the fundamental diagram, vehicle speed vᵤ is slower than speed vf. But once drivers have navigated around the truck, they can again speed up and transition to downstream state D. While this state travels at free flow, the vehicle density is less because fewer vehicles get around the bottleneck.
  Suppose that, at time t, the truck slows from the free-flow rate to v. A queue builds behind the truck, represented by state U.  Within the region of state U, vehicles more slowly, as indicated by the sample trajectory. Because state U limits to a smaller flow than state A, the queue will back up behind the truck and eventually crowd out the entire highway (slope s is negative).  If state U had the higher flow, there would still be a growing queue.  However, it would not back up because the slope s would be positive.
caption: A slow tractor creates a moving bottleneck.
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