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Reversible lane

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The Lions Gate Bridge from the south end in Stanley Park, Vancouver.
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The Lions Gate Bridge from the south end in Stanley Park, Vancouver.

A reversible lane (counterflow lane, or contraflow lane in transportation engineering [[wikt:nomenclature|nomenclature]]) is a lane in which traffic may travel in either direction, depending on certain conditions. Typically, it is meant to improve traffic flow during rush hours, by having overhead traffic lights and lighted street signs notify drivers which lanes are open or closed to driving or turning. Some people refer to non-physically-separated reversible lanes as suicide lanes due to many fatal accidents occurring when drivers failed to pay attention to the lights and lane markings and got into head-on collisions.

Reversible lanes are also commonly found in tunnels and on bridges, and on the surrounding roadways — even where the lanes aren't regularly reversed to handle normal changes in traffic flow. The presence of lane controls allows authorities to close or reverse lanes when unusual circumstances (such as construction or a traffic accident) require it to maintain orderly flow of traffic.

Contents

Signals and Markings

In the US, reversible lane markings are typically a dashed or broken double yellow line on both sides. Most often done on three-lane roads, the reversible lane is typically used for traffic in one direction at morning rush hour, the opposite for afternoon or evening, and as a turning lane at most other times. There is also a buffer period (half to one hour) between switches prohibiting traffic of any kind, in order to prevent collisions. Often times, lane control signals are placed over the roadway at regular intervals (within sight of each other) indicating which lanes are allocated to which travel direction; a red X indicates the lane is closed or reserved for the opposite direction; a green arrow indicates a permitted travel lane. The center lane is marked with either one of those (depending on time of day), and often a flashing yellow X at other times, becoming solid yellow before turning red. Other setups had double-turn-lane signs backlighted with white fluorescent lighting instead of the flashing yellow X.

Other streets with reversible lanes (including several in Washington, D.C.) simply have signs posted indicating what lanes are open to which direction when.

Separation of Flows

Some more recent implementations of reversible lanes use a moveable barrier to establish a physical separation between allowed and disallowed lanes of travel. In some systems, a concrete barrier is moved during low-traffic periods to switch a central lane from one side of the road to another; one example is the Coronado Bridge in San Diego, California or the seven lane Tappan Zee Bridge on the Hudson River in New York. Other systems use retractable cones or bollards which are built into the road, or retractable fences which can divert traffic from a reversible ramp. The two center lanes of the six-lane Golden Gate Bridge are reversible; they are southbound during morning rush hour and northbound at evening rush hour, and are demarcated with vertical flags.

Many urban freeways have entirely separate carriageways (and connecting ramps) to hold reversible lanes (the reversible lanes in such a configuration are often referred to as express lanes). Generally, traffic flows in one direction or another in such a configuration (or not at all); the carriageways are not "split" into two-lane roadways during non-rush periods. Typically, this sort of express lane will have fewer interchanges than the primary lanes, and many such roadways only provide onramps for inbound traffic, and offramps for outbound traffic.

Passing lanes

Typical striping on an old-style suicide lane setup in the United States.
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Typical striping on an old-style suicide lane setup in the United States.

Historically, a "suicide lane" has also referred to a lane in the center of a highway meant for passing in both directions. Neither direction had the right-of-way, and both directions were permitted to use the lane for passing. Head-on accidents were common. Very few of these setups are left, at least in the United States--though sometimes a similar layout exists, where three lanes are striped with two in one direction and one in the other, but traffic in the direction with one lane is allowed to cross the centerline to pass. However, this is not as dangerous, because one direction has clear right-of-way. They still however have 2-lane roads with 4-lane right-of-way where only the oncoming traffic in the opposite lane has to be checked as opposed to risking in a center lane.

Turn lanes

This is a typical 5-lane arterial equipped with a center-turn lane. These are often found in cities, towns and developed areas near cities. In the United States, the broken line is located on the inside of the lane. In Canada, the broken line is located on the outside.
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This is a typical 5-lane arterial equipped with a center-turn lane. These are often found in cities, towns and developed areas near cities. In the United States, the broken line is located on the inside of the lane. In Canada, the broken line is located on the outside.

Another type of center two-way lane is a center left-turn lane (for countries which drive on the right) or just center turn lane, a single lane in the center of the road into which traffic from both directions pulls to make a left turn. It is also used by drivers turning left onto the main road. While this is sometimes also called a "suicide lane", it is actually far safer, as car accidents occur at far lower speeds.

These roads are very common in suburban areas, and rather less common in rural areas. Many were divided highways before the median was demolished or otherwise filled with the turn lane.

This center lane can be used by emegencey vehicles like police cars, ambulance, and fire trucks to avoid traffic travelling in either direction.

Very rarely are drivers allowed to use the center lane of such a highway for passing slow-moving vehicles.

Examples

No (or minimal) lane controls

Lane controls and no (or minimal) physical separation

Trans-national

Australia Canada United Kingdom United States

Lane controls and physical separation by empty lane

Lane controls and physical separation by movable barrier

Third (reversible) carriageways on freeways

See also: Express lane

Entire roadway routinely reversed

The northern end of the Southern Expressway in Adelaide, South Australia, closed to south-bound traffic.
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The northern end of the Southern Expressway in Adelaide, South Australia, closed to south-bound traffic.

Oddities

See also

External links

 

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