Reversible lane
From Wikipedia, the free encyclopedia.
A reversible lane is a lane in which traffic may travel in both directions, 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 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 controls 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.
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 build 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.
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.
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Passing lanes
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
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.
Almost never is anyone allowed to use the center lane of such a highway for passing slow-moving vehicles.
Examples
Reversible lanes with no (or minimal) lane controls
Reversible lanes with lane controls, no (or minimal) physical separation
- The Sydney Harbour Bridge in Sydney, Australia (8 lanes total, 4 potentially reversible, 3 reversed daily)
- The Lions Gate Bridge in Vancouver, BC (3 lanes total, 1 reversible)
- The Golden Gate Bridge (6 lanes total, 2 reversible, median marked by flags which provide no obstacle to wrong-way traffic)
- There is at least one road in Sandusky, Ohio that has reversible lanes, for the purpose of allowing quick departure of Cedar Point guests.
- The Theodore Roosevelt Bridge in Washington, DC (carries Interstate 66). 7 lanes total, 1 reversible.
- Nicholasville Road (U.S. Highway 27) in Lexington, Kentucky has reversible lanes (lane signals, no physical separation) starting at its intersection with Rose Street at the University of Kentucky campus and ending at New Circle Road, the city's inner beltway. During morning rush hour, southbound traffic (away from the UK campus and downtown) is restricted to one lane between campus and Southland Drive, and two lanes from Southland to New Circle. Northbound traffic faces the same restrictions in the evening rush hour. During off-peak hours, an equal number of lanes are dedicated to traffic in each direction.
- The Chesapeake Bay Bridge near Annapolis, Maryland (5 lanes total, all marked reversible, 1 reversed at times during Summer travel, lanes may also be reversed during times of road work on the bridge)
Reversible lanes with lane controls, physical separation by empty lane
- Aston Expressway, Birmingham, England 7 lanes, only 6 used at any time - which lane is unused lane changes during peak periods.
Third (reversible) carriageways on freeways
- See also: Express lane
- Interstate 5 and Interstate 90 in Seattle, Washington
- Interstate 394 through Minneapolis, Minnesota and its western suburbs
- Interstate 395 through Washington, DC and its Virginia suburbs
- Interstate 15 in Northern San Diego, California
- Warringah Expressway in Sydney, Australia
- Interstate 90/Interstate 94 (aka Dan Ryan Expressway) in Chicago, Illinois
- Interstate 25 and US-36 in Denver, Colorado
Oddities
- Ontario provincial highway 17 has a railroad on the north side in Sault Ste. Marie, Ontario; the center lane on this corridor is restricted to westbound traffic. A double-yellow solid line separates the eastbound through lanes and the center lane.
- Rand McNally posts many 5-lane arterials in the countryside as divided highways on their maps.
- In New York, the Tappan Zee Bridge has a system of moveable barriers which are shifted by a special machine between each daily rush hour period.
