Bidirectional traffic

In transportation infrastructure, a bidirectional traffic system divides travelers into two streams of traffic that flow in opposite directions.

Bidirectional traffic is observed in a wide variety of applications, including aerodynamics; architecture; cellular automata; data; engineering; entomology; model theory; molecular biology; ornithology; pedestrian movement; and statistical mechanics.

Aerodynamics

In the design and construction of tunnels, bidirectional traffic can markedly affect ventilation considerations.

Modelling

Microscopic traffic flow models have been proposed for bidirectional automobile, pedestrian, and railway traffic.

Entomology

Bidirectional traffic can be observed in ant trails. As of recent years, this behavior has been researched for insight into human traffic models.

Human transportation

Airways

See also: Airway (aviation) and Right- and left-hand traffic § Vessels and aircraft

Aviation is normally separated by elevation, with east bound flights at odd thousand feet elevations and west bound flights at even thousand feet elevations. Above 28,000 feet only odd flight levels are used, with FL 290, 330, 370, etc., for eastbound flights and FL 310, 350, 390, etc., for westbound flights. Entry to and exit from airports is always one-way traffic, as runways are chosen to allow aircraft to take off and land into the wind, to reduce ground speed. Even in no wind cases, a preferred calm wind runway and direction is normally chosen and used by all flights, to avoid collisions. In uncontrolled airports, airport information can be obtained from anyone at the airport. Traffic follows a specific traffic pattern, with designated entry and exits. Radio announcements are made, whether anyone is listening or not, to allow any other traffic to be aware of other traffic in the area.

Railways

Main article: Double track

See also: Right- and left-hand traffic § Trains

A BNSF Railway intermodal train passes some maintenance of way equipment on the double track mainline in Prairie du Chien, Wisconsin.

In the earliest days of railways in the United Kingdom, most lines were built double tracked because of the difficulty of coordinating operations in pre-telegraphy times.

Roads

Main articles: Two-way street and dual carriageway

See also: Right- and left-hand traffic

A traffic sign in Victoria, Australia that reads "Drive on left in Australia"

Most modern roads carry bidirectional traffic, although unidirectional (one-way) streets are common in dense urban centres.

Bidirectional traffic flow is believed to influence the rate of traffic collisions. In an analysis of head-on collisions, rear-end collisions, and lane-changing collisions based on the Simon-Gutowitz bidirectional traffic model, Moussa concluded that "the risk of collisions is important when the density of cars in one lane is small and that of the other lane is high enough", and that "heavy vehicles cause an important reduction of traffic flow on the home lane and provoke an increase of the risk of car accident".

In a macroscopic theory proposed by Laval, the interaction between fast and slow vehicles conforms to the Newell kinematic wave model of moving bottlenecks.

Trails

Bidirectional traffic is the most common form of flow observed in trails, however, some larger pedestrian concourses exhibit multidirectional traffic.

Waterways

See also: Right- and left-hand traffic § Vessels and aircraft

See also

• Countercurrent exchange
• Microscopic traffic flow model
• Unidirectional traffic

Further reading

• US 5815161  "As shown, the two links 100, 102 have mutually opposite traffic directions. This means that in the joining, the complex road junction can get a bidirectional traffic indication."