Traffic bottleneck

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.

Traffic bottlenecks are caused by a wide variety of things:

Rubbernecking is an example of how bottlenecks can be induced by psychological factors; for example, vehicles safely pulled to the shoulder by a police car often result in passing drivers to slow down to "get a better look" at the situation.

Traffic flow theory can be used to model and represent bottlenecks.

Consider a stretch of highway with two lanes in one direction. Suppose that the fundamental diagram is modeled as shown here. The highway has a peak capacity of Q vehicles per hour, corresponding to a density of k_c vehicles per mile. The highway normally becomes jammed at k_j vehicles per mile.

Before capacity is reached, traffic may flow at A vehicles per hour, or a higher B vehicles per hour. In either case, the speed of vehicles is v_f (or "free flow"), because the roadway is under capacity.

Now, suppose that at a certain location x₀, the highway narrows to one lane. The maximum capacity is now limited to D’, or half of Q, since only one lane of the two is available. State D shares the same flow rate as state D', but its vehicular density is higher.

Using a time-space diagram, we may model the bottleneck event. Suppose that at time t₀, traffic begins to flow at rate B and speed v_f. After time t₁, vehicles arrive at the lighter flowrate A.

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