High occupancy vehicle lanes

High occupancy vehicle (HOV) lanes are a type of managed lane that can only be used by vehicles with more than one passenger. HOV lanes allow vehicles with multiple passengers to bypass traffic along congested corridors, and provide a speed and travel time reliability advantage over adjacent general purpose lanes.

Key characteristics




WSDOT regions

Other names

  • Carpool lanes
  • Diamond lanes
  • Bus-only lanes

Strategy description

High occupancy vehicle (HOV) lanes are a type of managed lane that is reserved for carpools, vanpools, buses, and/or other vehicles carrying multiple people. The purpose of the HOV lane is to improve person throughput on congested corridors and maximize the value of transit investments. HOV lanes improve person throughput by providing buses, vanpools, and carpools a speed and reliability advantage over single occupancy vehicles in the adjacent general purpose lanes. This provides an incentive for people to travel in higher occupancy vehicles. HOV lanes maximize the value of transit investments by supporting transit speed and reliability, which affect transit operating and equipment costs.

Depending on demand, use of HOV lanes can be limited to vehicles with two or more people, but can require three or more people in areas where congestion and transit frequencies are high.

HOV lane restrictions are sometimes limited to peak commuting hours or periods of higher traffic volumes. Outside of these hours these lanes can otherwise be used by general purpose traffic.

HOV lanes can be located as separated roadways, on a buffer-separated lane (with a buffer between the HOV lane and the general purpose lane), or on a non-separated lane. HOV lanes are often used on freeways and arterials. Standard HOV lanes on freeways are generally inside (left) lanes and on arterials are generally outside (right) lanes. HOV lanes are identified by signs along the roadway and diamond symbols painted on the pavement. Delineation of the HOV lane is typically with a solid white line.

When first entering a freeway, it is often necessary for high occupancy vehicles to cross over general purpose lanes to access an inside (left) HOV lane. In particularly congested areas direct access ramps can be constructed to allow high occupancy vehicles to enter a highway directly into an HOV lane. Queue bypass lanes can also be used for high occupancy vehicles to bypass isolated bottlenecks such as at ramp meters and signalized intersections.


The main areas of enforcement are around vehicles that falsely claim HOV status. Enforcement is conducted primarily by visual observations from highway patrol. Agencies are currently evaluating automated vehicle occupancy detection technology, but it is not currently reliable enough for widespread deployment.

When to use this strategy

HOV lanes make sense where roadways are congested, transit operating costs are increasing, and there is a desire to provide options for increased person throughput, reducing travel times and improving travel time reliability. In these situations, HOV facilities can provide travel benefits sufficient to encourage people to use transit services, vanpools, and carpools rather than driving alone. Support facilities such as park and ride lots and transit hubs can improve the effectiveness of HOV lanes. HOV lanes can be implemented by converting an existing general purpose lane to an HOV lane, converting a shoulder to an HOV lane, or when widening an existing roadway.

What you need in order to implement

Policy needs:

  • Regional policies on managed lanes, including HOV lanes, to identify the regional transportation vision, the goals and objectives for the specific corridor, and the primary purpose of the proposed HOV lane

Planning needs:

  • Analysis of current congestion levels, traffic composition (e.g. traffic volumes, origin-destination, transit service), physical roadway characteristics, and land use to evaluate the benefit of HOV lane conversion or construction

Coordination needs:

  • Extensive media and public outreach to provide education to users
  • Inter-agency coordination to develop policy, operations, and communications for HOV lanes across jurisdictions and/or systems
  • Law enforcement coordination to ensure driver compliance and to address potential violations

Equipment needs:

  • Automated license plate readers and CCTV video detection to identify vehicles accessing the HOV lanes improperly (where available)
  • Signage, including variable message signs where appropriate, to post HOV rules and display traveler information messages

Maintenance needs:

  • Regular testing and validation of the HOV lane system to confirm that all components are operating reliably and safely
  • Standard roadway maintenance activities
  • Continuous re-analysis to ensure operational performance targets are met

Agency resources needs:

  • Traffic engineers to place signs and other field elements, establish proper messaging, monitor its effectiveness, and make modifications to the system

Learn more about this strategy

WSDOT Design Manual, Chapter 1410 High-Occupancy Vehicle Facilities, July 2018 or latest draft

Federal Highway Administration (FHWA), Office of Operations, Guidance on High Occupancy Vehicle (HOV) Lanes

WSDOT, High Occupancy Vehicles (HOV) lanes website

WSDOT, Corridor Capacity Report (provides performance data on WSDOT’s current HOV network)

About key characteristics

Location notes:

Corridors and primary routes work best for HOV lanes because they have the vehicle capacity necessary for this strategy to be effective.

Cost notes:

HOV strategies range in sophistication and cost. Strategies that require new signs, sign structures, and barrier devices will have high costs. However, as an alternative to major roadway widening projects, HOV strategies that convert an existing general purpose lane are a relatively lower cost solution.

Technology notes:

In general there is little technology required for HOV lanes, however at some locations, variable messaging may be used to alert drivers of HOV rules and display traveler information messages.

Collaboration notes:

Collaboration for HOV lanes is high, requiring coordination between the roadway management agency and local partners including regional planning organizations, transit, county, and local agencies, and law enforcement.