Use dynamic lane merge systems to improve operations in long term construction zones.
Michigan Department of Transportation's experience with a dynamic lane merge system (DLM)
Made Public Date


United States

Intelligent Transportation Systems in Work Zones: A Case Study - Dynamic Lane Merge System


Michigan DOT (MDOT) rehabilitated a 13-mile stretch of I-94 in Southeast Michigan over two construction periods beginning in 2002. The $46 million dollar project involved considerable reconstruction ranging from concrete pavement repair and bituminous resurfacing to rehabilitation of 18 bridge structures. Given the considerable length of the construction zone and prolonged construction period, MDOT was concerned driver frustration could lead to aggressive driving prior to the merge point and within the construction zone. In an effort to address this concern head-on, MDOT deployed a dynamic lane merge (DLM) system to require early merging (prior to lane closures) and enforce DO NOT PASS zones upstream of the construction zone.

The DLM system utilized microwave radar sensors on five portable trailers, spaced 1,500 feet apart, to detect traffic volume, vehicle speed, and detector occupancy. When the system detected the freeway segment approaching a predefined threshold for operational conditions, the DO NOT PASS flashing signs were activated. Public safety officials were conveyed this information through a light on the back of the warning signs. When these lights were lit, officers would know to enforce no passing zones. The system would also shut down when conditions did not warrant dynamic enforcement of no passing zones.

Lessons Learned

The purpose of implementing the dynamic lane merge (DLM) system for this major construction project was to reduce aggressive driving at the merge point, maximize available capacity at the merge point just prior to dropping one lane out of three, reducing capacity losses due to increased headways at the work zone taper, and enhance traveler safety. The system accomplished the intended objectives and Michigan DOT (MDOT) was pleased with the results. Several lessons learned were noted:

  • Utilize a DLM system to help increase safety and reduce delay near work zones where lane closures are necessary.
  • Ensure that DLM trailer locations are wide enough to allow trailers to be moved in and out, and allow for safe placement off the roadway. This is also important for enforcement activities.
  • Consider frequency of changes to the work zone geometry and location before implementing a DLM system. It is better to use the DLM system at construction sites where the work zone geometry and location do not change frequently because such changes often require recalibrating the detectors. Long-term, large projects may have phases that are static, where the system can remain in place for a longer time.
  • Ensure that the system has line of sight between sensors for adequate communication. MDOT raised antennas on the trailers due to line of sight issues.
  • Ensure adequate access to sensor stations for maintenance purposes.
  • Identify stakeholders early in the planning stage and use a proactive approach to building public awareness of an ITS deployment. Successful techniques include meeting with stakeholders, holding press conferences, issuing news releases, and keeping local media up to date. MDOT used all of the above-mentioned techniques, and also met frequently with law enforcement early on to avoid miscommunication on overall system objectives and to keep them involved in the system planning and design.
  • Allow the driving community time to adapt to the DLM system. This will ensure that they will know how to comply with the regulatory signs in the DLM-controlled area. In addition, when changes in work zone roadway geometry are made, it is important to allow time for drivers to learn the new setup.
  • Ensure that the system has an adequate maintenance plan to avoid large amounts of system downtime.The implementing agency can meet maintenance needs solely through use of the vendor, or the agency can maintain the system with initial help from the vendor. Sensor power issues caused some small delays early on for MDOT.
  • Be aware that sensor stations may need to be reset manually when there are power interruptions.

MDOT was successful in deploying the dynamic lane merge system on I-94 as well as several other projects, to help smooth traffic flow and reduce aggressive driving just prior to the construction area. MDOT observed a decrease in aggressive maneuvers and average peak period travel time. These factors influenced both mobility and safety in a positive manner, and ultimately satisfied the goals of the deployment.

Intelligent Transportation Systems in Work Zones: A Case Study - Dynamic Lane Merge System

Intelligent Transportation Systems in Work Zones: A Case Study - Dynamic Lane Merge System
Publication Sort Date
Scriba, Tracy, and Tim Luttrell
Federal Highway Administration, U.S. DOT

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