Reversible lane

A reversible lane, also known as variable lane, dynamic lane, and tidal flow, is a managed 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 notifying drivers which lanes are open or closed to driving or turning.
Reversible lanes are also commonly found in tunnels and on bridges, and on the surrounding roadways – even where the lanes are not 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 mishap) require use of fewer or more lanes to maintain orderly flow of traffic.
There are similar setups with slightly different usages, although the terms may be commonly used interchangeably.
Contraflow Lane: Typically used to refer to a bus lane running against a one-way street through the opposite direction
Contraflow Lane Reversal: Typically used to refer to a temporary setup of a lane running opposite to normal during special times, such as emergency evacuations, sports tournaments, or road construction/repairs.
Reversible Lane: Typically used to refer to a lane specifically designed to facilitate different directional usage regularly, with changes sometimes as frequent as twice a day.
There are typically three types of reversible lanes:
While reversible lane is a commonly used term, other terms include variable lanes, dynamic lanes, and flex lanes.
Some more recent implementations of reversible lanes use a movable 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; some examples are the five-lane San Diego-Coronado Bay Bridge in San Diego, California, the seven-lane Alex Fraser Bridge on the Fraser River in Vancouver and the eight-lane Auckland Harbour Bridge across the Waitemata Harbour in Auckland, New Zealand. 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. Prior to the installation of a movable median barrier in January 2015, they were demarcated by vertical yellow markers placed manually in sockets in the roadway.
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.
Historically, the term "suicide lane" has also referred to a lane in the center of a highway meant for passing in both directions. Neither direction has the right-of-way, and both directions are permitted to use the lane for passing. In a similar layout, 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.
Passing lanes should not be confused with turning lanes. While they look similar, passing lanes are for highway overtaking, while turning lanes typically are used to stop and turn into a parking lot from a street.
2+1 roads have replaced some of these, mainly in Europe.
Another type of center two-way lane is a "two-way left turn lane" (TWLTL) or "center left-turn lane", or (for countries that drive on the right) "center turn lane" or "median turn lane", a single lane in the center of the road into which traffic from both directions pulls to make a left turn. This lane is also sometimes called a "suicide lane" for their notorious fatality rates, especially in the United States in settings with high traffic speeds (45 mph), and on roads with five or more lanes (typically two or three lanes in each travel direction with one center turn lane). However, some studies have found that converting high-speed four lane streets into three lane streets (one lane of traffic in each direction with a center turn lane) and lowering speed limits can result in improved safety, despite the use of a center turn lane, as traffic collisions occur at far lower speeds.
These roads are very common in suburban areas and less common in rural areas, though they are frequent around developed areas near Interstate Highway bypasses in the United States. Many were divided highways before the median was demolished or otherwise replaced by the turn lane. Many four-lane streets with a center double yellow line are being phased out in favor of 3- or five-lane streets with center turn lanes because the center lane allows for less disruption of traffic flow. For routes with moderate traffic, other movements involve downgrading four-lane undivided streets to three-lane streets with a turn-only center lane.
This center lane can be used by emergency vehicles like police cars, ambulance, and fire trucks to avoid traffic traveling in either direction. Drivers are not allowed to use the center lane of such a highway for passing slow-moving vehicles, except when funding or space constraints dictate use of it as a rush hour "travel lane" when traffic is largely asymmetric between a central business district and its suburbs. U.S. Route 13 near the Greenville, North Carolina, city limits is a rare instance of a posted warning sign that states "do not pass in center lane".
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In shopping centres and metro stations there may be an odd number of escalators, with one or more escalators running in different directions in different time of a day.