page_title: Managed lane
section_title: Reversible and contraflow lanes
hierarchical_section_title: Managed lane / Types of managed lanes / Dynamic lanes / Reversible and contraflow lanes
caption_attribution_description: English: en:Interstate 279 just outside of en:Pittsburgh.
context_page_description: A managed lane is a type of highway lane that is operated with a management scheme, such as lane use restrictions or variable tolling, to optimize traffic flow, vehicle throughput, or both. Definitions and goals vary among transport agencies, but managed lanes are generally implemented to achieve an improved operational condition on a highway, such as improving traffic speed and throughput, reducing air pollution, and improving safety. Types of managed lanes include High-occupancy vehicle lanes, High-occupancy toll lanes, express toll lanes, reversible lanes, and bus lanes. Most managed lane facilities are located in the United States, although HOV and bus lanes can be found in many other countries; outside of the US, many countries use active traffic management that manage all lanes of a highway.
context_section_description: Reversible lanes and contraflow lanes are commonly employed when there is little or no available right-of-way for the width of a highway to be increased. These types of managed lanes increase the highway's capacity in the direction of the flow of these lanes, which is typically the direction of travel of the majority of traffic during peak hours (e.g. into a city center in the morning, out of a city center in afternoons/evenings). Reversible lanes along expressways are typically separated from other traffic lanes by concrete barriers and incorporate multiple gates or barriers to prevent traffic traveling in the opposite direction from entering these lanes. Contraflow lanes are typically one or two lanes on one side of a dual-carriageway on which the direction of travel is reversed during certain hours. Contraflow lanes are generally separated from opposing traffic by plastic pylons or moveable jersey barriers.
  A limitation of implementing a reversible flow design is that it cannot serve congestion that may be present in the off-peak traffic direction. If such is the case, then some users, such as deadheading transit buses that need trip reliability to make a second peak direction run during the commute period, will be adversely impacted. All freeway reversible lanes must be separated by "Jersey" barriers in a high-speed roadway setting (which is not the case on arterial treatments). They are typically constructed in the median of freeway facilities and may be one, two or more lanes wide. These characteristics have several associated advantages and disadvantages. A facility that changes direction to serve morning and afternoon traffic can be an efficient solution since it allocates capacity specifically to the most congested direction of travel. Reversible lanes offer a much higher guaranteed level of service for transit since side friction from adjacent traffic is removed. Some locales, notably Houston, implemented reversible lanes to address the peak direction alone since width was not available to address both directions of travel. Adapting a reversible flow lane or roadway into a freeway typically requires rebuilding most bridges with center columns. A disadvantage of reversible lanes is the ongoing cost of daily surveillance and lane/ramp reversal activities. These treatments must be designed to prevent wrong way movements, requiring extensive and redundant ITS and traffic control device treatments for each opening, plus a staff compliment who must visually inspect the roadway prior to each opening period. Tolling and enforcement is made easier by the barrier environment in which a single field location can be identified to monitor and/or toll all traffic flow.
caption: Reversible HOV lanes in the center of Interstate 279 near Pittsburgh
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