Reversible lanes allow agencies to switch the direction of traffic flow during certain times and conditions. They are typically used during peak commuting hours to add capacity in one direction.
Reversible lanes help address traffic congestion by allowing agencies to switch the travel direction of one or more lanes when additional capacity is needed. Because they move capacity from one direction and give it to the other, they provide the most value for roads with highly directional congestion at certain times of day. Reversible lanes are typically operated on regular fixed schedules that reflect daily commuting patterns, but can also be activated for major events or incidents.
Some reversible lanes systems involve switching all the lanes of the roadway. For example, a four-lane roadway can have all four lanes operating in one direction and none in the other. Others incorporate movable physical lane dividers, often referred to as road zipper machines, to provide one direction of travel and an extra lane during peak-traffic hours while preserving some capacity for the other direction. In this case, a four-lane roadway might provide three lanes inbound and one lane outbound in the morning, to be reversed in the evening.
Modern reversible lanes are highly automated, with sign control and monitoring conducted remotely at a centralized transportation management center (TMC). Prior to activating the direction change, ground crews may perform a safety inspection of the reversible lanes and sweep for abandoned vehicles.
A highly automated switch-over process, such as with WSDOT’s operations for the I-5 reversible express lanes in Seattle, can take as little as 15 minutes to reverse the direction of the express lanes.
When to use this strategy
Reversible lanes make sense for arterial roads and highways that experience regular, significant imbalances in traffic demand by direction during peak periods (i.e., where excess capacity in one direction could be used in the other direction). Roads that may be used as emergency evacuation routes or for special events also benefit from reversible lane strategies.
- Increased use of existing infrastructure
- Delayed onset of congestion
- Smoother traffic flow
- Postpones or eliminates the need to add capacity through conventional lane additions
What you need in order to implement
- Development of agency design guidelines and standards for reversible lanes
- Inter-agency coordination to develop policy, operations, and communications to support coordinated operations of the reversible lanes.
- Systems engineering to describe the concept for the proposed system, key thresholds that will trigger activation of the system, and how it will operate under a variety of scenarios
- Design analysis to confirm that the necessary roadway equipment can be located and operated in a safe and effective manner
- Media and public outreach to educate road users. Reversible lane concepts have complex operating strategies new to most travelers
- Law enforcement coordination to ensure driver compliance and address potential violations
- Static and electronic signs to communicate reversible lane access status to drivers
- Barrier equipment, including gates and/or barrier-moving machines
- Traffic and/or incident detection to trigger lane reversals and lane closures
- Software to determine when lane reversals should occur and activate electronic signs and any field devices
- Closed-circuit television (CCTV) and redundant monitoring components to verify that the system is operating safely
- Regular testing and validation of the dynamic lane assignment system to confirm that all components are operating reliably and safely
Agency resources needs:
- Traffic engineers to place signs and other field elements, establish proper messaging, monitor its effectiveness, and make modifications to the system
- Traffic management center operators to operate and monitor the reversible lanes system
- For non-automated systems and those requiring additional safety redundancies, ground crews to perform regular safety sweeps of the express lanes prior to activating the reversal
Learn more about this strategy
Texas A&M Transportation Institute, Mobility Investment Priorities, Reversible Traffic Lanes (PDF).
Federal Highways Administration (FHWA), Freeway Management and Operations Handbook, Chapter 8, Managed Lanes, 2011.
About key characteristics
Reversible lanes are appropriate for highway corridors and major urban arterial roads with regular, significant imbalances in traffic demand during certain times.
Reversible lanes require investments in high-cost elements including signs, sign structures, barrier devices, and system-wide CCTV monitoring systems. However, reversible lanes may be a relatively lower-cost solution than major roadway widening projects.
Reversible lanes require electronic signs, sensors to measure traffic volumes and speeds, monitoring cameras, and sophisticated central software to manage the application.
Collaboration may involve relatively few agencies, including law enforcement and local traffic agencies, but the level of collaboration required is high due to the safety-critical nature of this strategy.