Dynamic lane assignment

Dynamic lane assignment strategies repurpose road space based on current or expected demand conditions in order to improve the efficiency and safety of the transportation system. Dynamic lane assignment strategies include reversible lanes on highways and arterials, merge (or junction) control on highway ramps, and part-time highway shoulder use.

Key characteristics




WSDOT regions

Strategy description

Dynamic lane assignment is a category of managed lane strategies that involve reallocating road space in response to changes in demand in order to use existing infrastructure most efficiently. This approach can function as an alternative to constructing more roadway by providing additional capacity to certain kinds of traffic at certain times.

WSDOT’s Managed Lanes policy document demonstrates ways to increase capacity without adding new general-purpose lanes. 

Three categories to make best use of existing road space:

  • Road pricing as a means to regulate demand
    Examples include traditional toll lanes and toll lanes that adjust price based on congestion levels
  • Vehicle eligibility as a means to give preference or exclude certain vehicle types
    Examples include high-occupancy vehicle (HOV) lanes that are reserved for vehicles with a driver and one or more passengers, transit lanes, and truck lane restrictions.
  • Access control as a means to better utilize available and unused roadway capacity 
    Examples include reversible lanes and part-time shoulder use, dynamic lane assignment strategies fall into this category

Dynamic lane assignment strategies can range in sophistication and level of automation. Low-tech implementations include setting out traffic cones and dispatching safety officers to create a temporary shuttle bus lane to serve a special event, for example. High-tech implementations, e.g., automated merge control systems, may use real-time traffic and incident detection to activate electronic lane control signs to shift drivers out a lane that is blocked or congested ahead.

Communicating lane assignments to travelers

Travelers are typically informed of the current lane assignment via one or a combination of the following three methods:

  • Static signs (e.g., signs that allow freeway shoulder access that during certain hours)
  • Electronic signage (e.g., lane use signs and variable message signs that can be activated automatically or remotely)
  • Moving physical barriers (e.g., gates at either end of a reversible lane or road zipper machines that move concrete lane dividers to provide one direction of travel an extra lane during rush hours or temporarily during construction work.)

When to use this strategy

Dynamic lane assignment makes sense for roads with 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). It also applies for temporary or nonrecurring conditions, such as for roads that may be used as emergency evacuation routes, special events, or for construction and maintenance projects that may require temporary lane closures or lane shifts. Dynamic lane assignment strategies should also be considered as a lower cost alternative to constructing additional roadway capacity.

Strategy benefits:

  • Increased use from existing infrastructure
  • Delayed onset or reduced duration of congestion
  • Smoother traffic flow
  • Improved work zone safety through more flexible lane assignment

What you need in order to implement

Dynamic lane assignment comprises a broad range of strategies, each with their own implementation requirements. In general, however, the following considerations are applicable to any dynamic lane assignment strategy.

Planning needs:

  • Operational analysis to determine appropriate dynamic lane assignment strategy or combination of strategies to address the traffic challenges
  • Roadway capacity analysis to determine the amount of repurposable road space available based on current or expected demand conditions
  • Systems engineering to describe the concept for the proposed system, key thresholds that will trigger activation of the system, how it will operate under a variety of scenarios, and the roles and responsibilities
  • Design analysis to confirm that the necessary roadway equipment can be located and operated in a safe and effective manner

Coordination needs:

  • Media and public outreach to provide education to users, given that dynamic lane assignment concepts are new to most travelers and include complex operating strategies
  • Inter-agency coordination to develop policy, operations, and communications for dynamic lane assignment strategies across jurisdictions and/or systems
  • Law enforcement coordination to ensure driver compliance and address potential violations

Equipment needs:

  • Static and/or electronic signs to communicate lane usage to drivers
  • Barrier equipment, including gates and/or barrier-moving machines
  • Traffic and/or incident detection as input into dynamic lane assignment operational strategies
  • Software to interpret traffic and incident data, determine dynamic lane assignment operations, and activate electronic signs and any field devices
  • Closed-circuit television (CCTV) and redundant monitoring components to verify that the system is operating safely

Maintenance Needs:

  • 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 dynamic lane assignment system

Learn more about this strategy

WSDOT Design Manual, Chapter 1400 Managed Lanes, July 2018 or latest draft.

National Cooperative Highway Research Program (NCHRP), Report 835 Guidelines for Implementing Managed Lanes, 2016.

Federal Highway Administration (FHWA), Managed Lanes: A Primer.

Transportation Research Board, Circular E-C153 Dynamic Traffic Assignment: A Primer, 2011 (PDF).

About key characteristics

Location notes:

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

Cost notes:

Dynamic lane assignment 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, dynamic lane assignment strategies are a relatively lower cost solution.

Technology notes:

Dynamic lane assignment strategies range in sophistication and technology needs, but generally have high technology requirements. Typical strategies require electronic signs, sensors to measure traffic volumes and speeds, monitoring cameras, and sophisticated central software to manage the application.

Collaboration notes:

Collaboration with other traffic agencies is relatively low because dynamic lane assignment strategies are typically implemented on a single agency’s roadway. However, coordination with law enforcement to ensure driver compliance is critical given the safety-critical nature of these strategies.