A variable speed limit system deployed at a work zone on I-96 in Lansing, Michigan contributed to a decrease in the number of high-speed vehicles in the work zone.
Made Public Date


United States

Field Test of Variable Speed Limits in Work Zones (In Michigan), Final Report

Summary Information

During the summer of 2002, the Michigan DOT deployed a prototype variable speed limit (VSL) system on a segment of I-96 in Lansing. The VSL system was comprised of seven trailers with microwave vehicle detectors, dynamic message signs (DMS), remote processing units, solar power, short-range radio communication between trailers, cellular telephone modems for remote data retrieval, and a pager system for law enforcement personnel to determine displayed speed limits.

The seven trailers were deployed at half-mile to one-mile intervals along a work zone on I-96 during a before-and-after study. In the "before" period, the DMS were covered with static 50 mi/hr speed limit signs. In the "after" period, the DMS were uncovered and the VSL system was activated. The system monitored traffic conditions and displayed speed limits ranging from 40 to 70 mi/hr based upon roadway geometry, the prevailing speed, the day of week, and the type of construction underway. For both periods, traffic data were collected from the microwave vehicle detectors and from pneumatic tube vehicle detectors installed by the Michigan DOT.


An anecdotal assessment of crash data indicated that no crashes appeared to be directly associated with deployment of the system. Of the small number of crashes, most occurred in the direction of travel that was not controlled by the VSL system. Thus, it was concluded that the system did not increase crash frequency.

Field Test of Variable Speed Limits in Work Zones (In Michigan), Final Report

Field Test of Variable Speed Limits in Work Zones (In Michigan), Final Report
Publication Sort Date
Michigan DOT and Michigan State University

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