Knowledge Resources

In the summer 2002 and 2003, the Michigan DOT rebuilt a 13.5-mile section of I-94 in the suburbs of Detroit. To help smooth traffic flow, the DOT deployed a dynamic lane merge (DLM) system. The system was designed to regulate merging movements in transition areas where lane configurations changed from three lanes to two lanes. A series of five DLM trailers equipped with microwave traffic sensors, wireless communications, and "Do Not Pass When Flashing" static signs with flashing beacons were installed upstream from the work zone at 1,500 foot increments. When traffic queues developed on the approach and traffic conditions degraded beyond pre-set threshold limits, the system automatically activated flashers on DLM signs to promote early merging. Once activated, the flashers continued operating for a minimum of five minutes. In addition, a state patrol officer was on site to promote compliance, several static signs showing the message "Do Not Pass" and "Form Two Lanes" were posted on the approach, and a portable dynamic message sign with a large arrow and a "Merge" message was strategically placed in the transition area.

The DLM system was most effective at peak hour traffic volumes of 3,000 to 3,500 vehicles per hour. The study found that if traffic volumes were consistently below or above these levels the system would have limited effectiveness. With low traffic volumes, merging control would most likely not be needed; and with higher traffic volumes, the resulting queues lengths would be so long that the flashers would operate continuously and the automated system would not be needed.

Probe vehicle runs and traffic data were collected by Michigan DOT and Wayne State University. The following impacts were highlighted.

• During the afternoon peak period, the average number of aggressive driving maneuvers per travel time run decreased from 2.88 to 0.55. During the morning peak period there was no change.
• During the four months prior to activation, an average of 1.2 crashes per month occurred. For the two month period the system was active, no crashes were reported.
• Michigan DOT observed less traffic disruption due to queuing and a decrease in variance between vehicle speeds.