Dynamic Merge Control

Dynamic merge control, or junction control, automatically manages the entry of vehicles into merge areas. Agencies can change the amount of access based on traffic demand by using light-up signs to open or close an extra lane at an exit or entrance ramp.

A potential U.S. application is at a two-lane entrance ramp where the left lane of the ramp merges with the outside lane of the freeway. With dynamic merge control, either the outside freeway lane or the left lane of the entrance ramp would be closed by dynamic signs prior to the merge (depending on traffic volume).

Target Market

• Freeways or roads with a lot of congestion and merging vehicles.
• Freeways with available space on main lanes prior to a merge area that can be borrowed.
• Roads where traffic volumes on two connecting roads peak at different times.

How Will This Help?

• Delays or stops the start of congestion by increasing capacity, encouraging a smoother flow of traffic, and improving travel time reliability.
• Improves safety by reducing crashes caused by merging.
• Increases throughput by temporarily increasing capacity.

Conditions that warrant dynamic merge control include:

• Large merging volumes (more than 900 vehicles per hour).
• Available space on general-purpose lanes prior to the interchange that can be borrowed without generating stop-and-go traffic.
• Traffic volumes that peak at different times on the general-purpose lanes and merging lanes.

Dynamic merge control works best on roadways that have:

• Active response to incidents in the corridor.
• Existing operations improvements.
• Communication connections to a traffic management center.
• Potential for combined shoulder use.

The following are key factors that can support successful deployment:

• Effective dynamic merge control uses lane control signals on the main lanes and merging lanes of a freeway to close a lane as needed. Overhead signs should be installed well ahead of the location to ensure advance warning to drivers.
• An ideal system deploys the strategy based on roadway conditions without requiring operator intervention.
• A bypass lane should be created for emergency vehicles or transit and other exempt users. Dynamic merge control can be used in conjunction with temporary shoulder use as long as the appropriate overhead signs and lane control signals are employed.

Who Is Responsible?

The local state department of transportation office is responsible for developing and maintaining dynamic merge control. This agency should:

• Determine the need for the strategy.
• Confirm the availability of the needed right of way so that signs can be installed at regular intervals for best visibility.
• Provide adequate infrastructure for the traffic management center and other roadside devices.

Project Time Frame

The lengths of dynamic merge control projects differ based on the scale of the problem and the available infrastructure. The systems should have adequate connections to the local traffic center and other supports, and policies should be in place. Since some additional signage will be required, a typical deployment may take between one and two years to begin.

Cost

The cost of implementing dynamic merge control within a corridor varies depending on the existing infrastructure and whether temporary shoulder use and/or variable speed limits will be used in conjunction with the merge control.

Data Needs

Standard traffic data should be evaluated to determine the need for dynamic merge control and the best way to operate it. These traffic data include:

• The maximum capacity of upstream general-purpose lanes.
• Traffic volumes on general-purpose lanes and merging ramps.
• Travel speeds on general-purpose lanes and merging ramps.
• Incident presence and location.