Reversible lane

A reversible lane (British English: tidal flow) 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.

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.

Separation of flows
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 Tappan Zee Bridge on the Hudson River in New York 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, and are 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.

Passing lanes


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.

2+1 roads have replaced some of these in Europe and North America.

Turn lanes / flush median




Another type of center two-way lane is a center left-turn lane (for countries which 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. While this is sometimes also called a "suicide lane", it is actually far safer, 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. Many were divided highways before the median was demolished or otherwise filled with the turn lane. Many four-lane streets with a center double yellow line are being phased out in favor of 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.

No (or minimal) lane controls

 * Connecticut Avenue in Washington, D.C.
 * Chain Bridge in Washington, D.C.
 * Bailey Bridge, in Coquitlam, B.C.

Lane controls and no (or minimal) physical separation

 * Canada
 * The Lions' Gate Bridge in Vancouver (3 lanes total, 1 reversible)
 * The Angus L. Macdonald Bridge, Chebucto Road and the Herring Cove Road in Halifax, Nova Scotia (3 lanes total, 1 reversible)
 * Jarvis Street in downtown Toronto (5 lanes total, centre lane reversed daily for AM/PM rush hours)
 * The Champlain Bridge in Ottawa (3 lanes total; 1 reversible)
 * Sherman Access and Sherman Cut in Hamilton, Ontario (2 lanes, both reversible)
 * The George Massey Tunnel in Delta and Richmond, B.C. (4 lanes total, 2 reversible, with access controlled by gates)
 * Connors Road in Edmonton (4 lanes, 3 reversible)
 * McDougall Hill in Edmonton
 * 127th Street from 132 Avenue to Yellowhead Trail
 * 170th Street from north of 137th Avenue to Levasseur Road in Edmonton (3 lanes total, 1 reversible)
 * 97th Street from 118th Avenue to 127th Avenue in Edmonton (7 lanes total, 3 reversible)
 * Centre Street from 20th Avenue N to 6th Avenue S in Calgary (4 lanes total, 2 reversible; standard configuration is 2 out, 2 in; morning rush is 1 out, 3 in; and evening rush is 3 out, 1 in)
 * 10th Street NW / 9th Street SW from 5th Avenue NW to 4th Avenue SW in Calgary (4 lanes total, 2 reversible; standard configuration is 2 out, 2 in; morning rush is 1 out, 3 in; and evening rush is 3 out, 1 in)
 * Park Avenue in Montreal, five lanes total, centremost lane is reversible, sidemost lanes are reserved for public transport during rush hour; morning rush is 2 in, one out (not including bus lanes), evening rush is reversed
 * Champlain Bridge in Montreal, rush hour bus lanes
 * Jacques Cartier Bridge in Montreal, five lanes total, two for both directions, one rush hour central reversible lane
 * During the 2010 Winter Olympics, British Columbia Highway 99 was subject to lane control in three-lane sections of the highway, via signs on the side of the road that were changed manually.
 * United Kingdom
 * The A38 road across the Tamar Bridge and through the Saltash Tunnel in Saltash, England. The middle lane is reversible, allowing for control of traffic flows in holiday periods and during rush hour.
 * The A61 Queen's Road in Sheffield, England, although it is a very short section (4 lanes total, 1 reversible: allowing for either 3 out, 1 in, or 2 out, 2 in).
 * The A470 North Road in Cardiff, Wales, A section of around 1 mile long between the Maindy Road Junction and College Avenue where the road drops from a dual two-lane to a three-lane section. One lane is always dedicated to Northbound (out of town) traffic, and one lane to Southbound (city centre bound traffic) with the centre lane reversing depending on the time of day - i.e. in the morning 2 lanes into the city, 1 lane out, in the evening 2 lanes out of the city, 1 lane in.
 * The A15 in Lincoln (Canwick Road) has a short three-lane section of tidal flow.

Alabama Alaska Arizona California Connecticut Florida Georgia Kentucky Indiana Maryland Michigan Nebraska New Jersey
 * United States
 * In Montgomery, Norman Bridge Road through the Garden District and Old Cloverdale has a center lane with reversible markings and traffic flow lights between Burton Street and Legrand Place.
 * The Anton Anderson Memorial Tunnel between Portage and Whittier is a 13,300 feet (4,050 m) long, reversible single lane tunnel, shared between vehicular traffic and trains. The direction of traffic alternates every 15 minutes, with periods allowed for train traffic each day.
 * In Phoenix on 7th Avenue between McDowell Road and Northern Avenue, and 7th Street between McDowell Road and Cave Creek Road/Dunlap Avenue. On both roads, the lane configuration is 2 southbound and 3 northbound, with the center lane open for southbound traffic between 6-9am and open to northbound traffic between 3-6pm. Left turns are prohibited from the reversible lane at most arterial and collector street intersections during these hours but still allowed at driveways and non-signaled street intersections.
 * The Golden Gate Bridge (6 lanes total, 2 reversible, vertical median markers provide minimal physical separation) connecting San Francisco with suburban Marin County
 * Lafayette Street in Santa Clara - the center lane is used for northbound traffic on weekday mornings, southbound traffic for weekday afternoons, and as a center turning lane at other times.
 * The Baker-Barry Tunnel, one of only two means of access to the Marin Headlands from U.S. Route 101 in Marin County, is not wide enough to accommodate bidirectional traffic. It consists of a single reversible lane for automobiles and two bicycle lanes.  The direction of automobile traffic alternates every five minutes, controlled by a traffic light at each end of the tunnel.  The bicycle lanes, one for each direction, are located on either side of the reversible lane; buttons on either side of the tunnel trigger flashing signs alerting drivers entering the tunnel to the presence of cyclists.
 * Asylum Avenue in Hartford
 * Bay Street in Jacksonville
 * South Atlanta Street in Roswell, Georgia as part of Georgia State Route 9 is 3 lanes between with overhead lane-use control signals Marrietta Highway (SR 120) and the Chattahoochee River.
 * Northside Drive in Atlanta: the center lane of three is reversed using overhead lane-use control signals.
 * Vineville Avenue in Macon: the center lane of three is reversed using overhead lane-use control signals.
 * The Clay Wade Bailey Bridge in Covington (3 lanes total, 1 reversible)
 * Nicholasville Road (U.S. Highway 27) in Lexington, 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, as well as the hours before UK football home games, 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 and immediately after football games. During off-peak hours, an equal number of lanes are dedicated to traffic in each direction.
 * Baxter Avenue and Bardstown Road (U.S. Highway 31E) in Louisville have reversible lanes (lane signals without any physical separation) for 2½ miles starting at their intersection with Lexington Road in the north and ending at Douglass Boulevard in the south. This stretch of road has four lanes, but on-street parking frequently restricts traffic to one lane in each direction outside of rush hours. During rush hours, parking is prohibited north of Douglass Boulevard. Southbound traffic leaving downtown Louisville is restricted to one lane during the morning rush hour, with northbound traffic having the same restriction during the evening rush hour. Also, the lane immediately to the left of rush-hour through traffic becomes a dedicated left-turn lane. Electronic signs over the roadway alert motorists to the traffic flow dedication of each lane.
 * In Indianapolis, Fall Creek Parkway North Drive between Central Avenue and Evanston Avenue has 5 lanes (7 in some sections) with 1 lane marked as reversible. Configuration is typically designed to allow for 3 in, 2 out during morning rush hours, and 2 in, 3 out during afternoon rush hours.  Due to Fall Creek Parkway's proximity to the Indiana State Fairgrounds, lane configurations change periodically to facilitate traffic flow during events at the fairgrounds.
 * The Chesapeake Bay Bridge near Annapolis (5 lanes total, all marked reversible, 1 usually reversed for normal peak traffic). However, due to its dual spans, when there are 2 eastbound lanes and 3 westbound the opposing sides are completely divided, this is the usual configuration.
 * The Hanover Street Bridge in Baltimore has 5 lanes total marked reversible, with 1 usually reversed for normal peak traffic).
 * Georgia Avenue in Silver Spring has 7 lanes. During most hours, the center lane is marked with a yellow lit X as a left turn lane for both directions. During morning and evening rush hours, the lane is marked with a down facing green arrow – southbound in the morning, northbound in the evening – or a red X – northbound in the morning, southbound in the evening – and left turns are prohibited.
 * Colesville Road in Silver Spring has 6 lanes. During off-rush hours, three lanes go in each direction. During morning rush hours, four lanes (marked with green arrows) go southbound, while northbound (marked with Xs in those lanes) is relegated to two lanes. During afternoon rush, the process is reversed.
 * The Mackinac Bridge near St. Ignace treats the passing lane of the southbound side as a temporary northbound lane during the Labor Day bridge walk, at which time the northbound side is used for pedestrians.
 * Dodge Street between Turner Boulevard and 68th Street in Omaha: no physical separation; lanes marked with overhead lane-use control signals. Center lane direction is eastbound from 5:50am-9:00am and westbound from 9:00am-5:50am.
 * Farnam Street between Saddle Creek Road and 57th Street in Omaha: no physical separation; lanes marked with lane-use control signals and LED signs. On weekdays the direction is one-way eastbound 7am-9am, and one-way westbound 4pm-6pm.
 * Since 1970, the Lincoln Tunnel Approach and Helix in Hudson County, New Jersey supports an "XBL", or Exclusive Bus Lane, on New Jersey Route 495 during the weekday morning peak period (approximately 6:00 a.m. - 10:00 a.m.).  Eastbound buses travel in this reversible lane to the approach to the toll plaza at the Lincoln Tunnel, at the other end of which is the Port Authority Bus Terminal in Midtown Manhattan in New York City. The lane is fed by the New Jersey Turnpike at Exits 16E and 17, and the western terminus of New Jersey Route 3. Both the tunnel and terminal are owned and operated by the Port Authority of New York and New Jersey, the bi-state agency that also operates the 2.5 mi reversible, express bus lane along the left lane of three westbound lanes. The XBL serves over 1,800 buses, which transport more than 65,000 persons, each morning and is a major component of the morning "inbound" commutation crossing the Hudson River.   Over 100 bus carriers utilize the Exclusive Bus Lane. New Jersey Transit operates numerous interstate bus routes through the Lincoln Tunnel, as do numerous regional and long distance companies.
 * Each of the travel lanes in the Lincoln Tunnel's center tube is reversible. In general, both of the lanes, including one "XBL" (Exclusive Bus Lane), serve Manhattan-bound traffic during the weekday morning rush hour, both of the lanes serve New Jersey-bound traffic during the weekday evening rush hour, and one lane is provided in each direction during other time periods.
 * The Walt Whitman Bridge, Ben Franklin Bridge and Commodore Barry Bridge over the Delaware River between New Jersey and Pennsylvania use moveable medians, to create zipper lanes.

New York North Carolina Ohio Pennsylvania Texas Virginia
 * Delancey Street in Manhattan has two lanes on the eastbound side adjacent to the median used for westbound traffic in the morning rush hour between the Williamsburg Bridge and Allen Street. All traffic in these lanes must continue to and then turn left onto Allen, during these times left turns are prohibited from the regular westbound roadway onto Allen Street.
 * Manhattan Bridge (New York City) lower level has three lanes, which can have all lanes used in one direction or reversible with two lanes one way and the other for the opposite direction.
 * The upper level of the Queensboro Bridge in New York City has four lanes and can have all flowing outbound (PM peak), or two lanes each direction in normal configuration.
 * The Mid-Hudson Bridge in Poughkeepsie, New York has a reversible center lane used during rush hour.
 * East 7th Street in Charlotte
 * Tyvola Road in Charlotte
 * Since the closure (2005) and implosion (2007) of the former Charlotte Coliseum (II), this road is no longer reversible; all lights have been removed and lane signs are permanent.  It was designed this way for Coliseum traffic from NBA games and concerts.
 * U.S. Route 29 in Charlotte
 * This road is the access road to Charlotte Motor Speedway from the city, and links to Interstate 485. It is used for any events at the Speedway.
 * High Point Road in Greensboro
 * The lanes have rarely been reversed (even for special events that cause traffic to back up for miles) and the city has finally removed them, converting the street to three south-bound lanes, two north-bound lanes, and one left-turn lane.
 * Edwards Mill Road in Raleigh
 * At least one road in Sandusky has reversible lanes, for the purpose of allowing quick departure of Cedar Point guests.
 * The Liberty Bridge near the southern terminus of I-579 in Pittsburgh has 4 lanes, all of which are potentially reversible, and 2 of which are reversed based on rush-hour times.
 * The West End Bridge in Pittsburgh has 4 lanes, which are all potentially reversible.
 * West General Robinson Street near Heinz Field in Pittsburgh has 4 lanes, and 2 are reversible.
 * West Alabama Street and North Main Street in Houston – both are three-lane streets, which operate in a 2 in, 1 out configuration during the morning rush, a 1 in, 2 out configuration during the evening rush, and a 1 each way + two-way left turn lane at other times.
 * Interstate highway 10 and US highway 290 in Houston have contraflow HOV lanes intended to help ease rush hour traffic.
 * Washington Boulevard (State Route 237) in Arlington County between 13th Street and Wilson Boulevard - this one-block section has only 3 lanes with the center lane reversible by overhead light up indicators.

Lane controls and physical separation

 * The A38(M) motorway (also known as the Aston Expressway) in Birmingham, England. The road connects the city centre with Spaghetti Junction on the M6. It is a 2-mile, 7-lane section of motorway with no central reservation, and a lower than usual speed limit of 50 mph. Constructed in 1971, it was the United Kingdom's first contraflow road. Overhead lane control signals allow for 4 lanes in and 2 out in the morning rush hour, reversed in the evening, and 3 lanes each way at all other times. One dividing lane is closed to traffic at all times, and motorcycles are permanently prohibited from using the central, red-surfaced lane (with a fixed sign) owing to its use as an off-camber drain. The lane control signals can be set to allow travel in either direction for any lane in exceptional circumstances, which has been used for single-lane, reduced-speed running in each direction (or 2+1 with no divider) during road work, allowing the expressway to remain largely open even during major repairs. However, the 7-lane section splits at both ends to fully divided sets of 4x2 lane slip roads, with the central red lane ending in a barrier, so full use of this flexibility is uncommon and occasional overnight closure is required.
 * U.S. Route 78 in Snellville, Georgia, United States, has 6 lanes in total. This occurs from the limited access portion through Stone Mountain Park to Georgia State Route 124 (Scenic Highway) for several miles. The middle two lanes were reversible (usually occurring during rush hour) with a varying lane always reserved as a center turn lane; hence 3 lanes were used for one direction of travel and 2 for the other. Example of an intersection on U.S. 78. However, due to rising traffic volumes during peak hours that made traffic flows equivalent, the reversible lane system was removed in 2009.
 * The Caldecott Tunnel between Oakland, California and Contra Costa County, California has three separate bores, with the middle bore switching direction twice daily for rush hour traffic.
 * The Elbe Tunnel near Hamburg, Germany is part of the Bundesautobahn A7 and has four separate bores, of which two can be switched to allow travel either in each direction or unidirectionally.

Lane controls and physical separation by movable barrier

 * Benjamin Franklin Bridge, Walt Whitman Bridge, and Commodore Barry Bridge in Philadelphia, PA
 * Tappan Zee Bridge in New York
 * Theodore Roosevelt Bridge in Washington, D.C.
 * Auckland Harbour Bridge in Auckland, New Zealand
 * San Diego-Coronado Bay Bridge in San Diego, California (part of California Route 75)
 * Southeast Expressway in and near Boston, Massachusetts
 * A reversible lane, also called a zipper lane, is in use on eastbound Interstate H-1 for traffic heading from Leeward Oahu to Pearl Harbor.  It is open from 5:30 to 8:30 a.m.
 * Doyle Drive (U.S. Route 101) in San Francisco (until completion of Presidio Parkway, scheduled for 2015)

Third (reversible) carriageways on freeways

 * Bundesautobahn 7, New Elbe Tunnel, Hamburg, Germany (actually two reversible carriageways, plus two fixed)
 * Warringah Expressway in Sydney, Australia
 * Interstate 5 in Seattle, Washington, and Interstate 90 between Seattle and Bellevue, Washington
 * Interstate 15 in northern San Diego, California
 * Interstate 25 and US-36 in Denver, Colorado
 * Interstate 394 through Minneapolis, Minnesota and its western suburbs
 * Interstate 90/Interstate 94 (Kennedy Expressway portion) in Chicago, Illinois
 * Interstate 70 through St. Louis, Missouri
 * Lee Roy Selmon Expressway from Brandon to Tampa, Florida
 * Interstate 64 in Norfolk, Virginia (center carriageway reserved for HOV traffic during rush hour)
 * Interstate 395 and Interstate 95 through Washington, D.C. and its Virginia suburbs (center carriageway reserved for HOV traffic during rush hour)
 * Lincoln Tunnel between Weehawken, New Jersey and New York, New York has three tubes with two lanes each. The center tube carries two lanes in peak direction weekdays (with a reserved inbound bus lane during the AM rush period) and a single lane each direction off-peak (nights, weekends, holidays).
 * Multiple freeways in Houston have reversible center HOV lanes operated by Houston METRO.
 * Interstate 93 through Boston, Massachusetts

Entire roadway routinely reversed

 * The Anchieta/Imigrantes highway system in Brazil contains the world's longest fully reversible road (The Imigrantes variant at a length of 58.5 km). It comprises a total of 10 lanes distributed over 4 separate roadways (3+3+2+2), each of which can be reversed. Traffic flow is unidirectional on up to three roadways at a time, in different combinations, depending on demand. Since this highway system is the only quick route from São Paulo to the beach, the majority of the traffic on Fridays and Sundays are cars on weekend trips, creating highly asymmetrical demand.
 * The Southern Expressway in Adelaide, South Australia is the world's longest exclusively one-way reversible road, spanning 21 km though the city's southern suburbs. It changes direction to carry peak hour traffic to the city centre in the morning and away from the city in the evening. On weekends the directions are reversed. Works are currently occurring to convert the Expressway to carry 2-way traffic and are expected to be completed in 2014.
 * In Washington, D.C., the Rock Creek and Potomac Parkway between the Lincoln Memorial and Calvert St. is converted from two lanes in each direction to one-way southbound in the morning and one-way northbound in the evening rush hour Monday through Friday, excluding federal holidays. The P Street exit, usually unavailable northbound, is an allowed left exit in the evening. South of Virginia Avenue, two lanes are closed during rush hours to facilitate the merge to or from Virginia Avenue. There are no overhead markings, but police barricades block wrong-way entrances to the roadway.
 * In Washington, D.C., parts of 15th Street NW and 17th Street NW are one-way during certain hours. There are no overhead markings on either road.
 * Canal Road in Washington, D.C. (between Foxhall Road and Arizona Avenue)
 * In Hong Kong, most vehicular tunnels are dual tube. In the early hours one of the tubes will be closed, and one of the lanes in the other tube carries reversed traffic.