During the 2002 and 2003 summer construction season, the Michigan Department of Transportation embarked on a large-scale reconstruction project along Interstate 94 (I-94) near Detroit. The reconstruction project costing a total of $46 million involved 13.5 lane miles in both directions. To optimize throughput and reduce aggressive driving in the lanes leading to the work zone, the Michigan DOT deployed a dynamic lane merge (DLM) system. The DLM system used electronics and communications equipment to monitor traffic flow and to regulate merge movements and require early lane merging as traffic queues formed at approaches to lane closures.
The system included five DLM trailers, spaced 1,500 feet apart and in advance of the work zone. Each trailer had a flashing “Do Not Pass” sign, wireless radio communication equipment, and a power source rechargeable via a solar power system. The DLM system used wireless radio communication equipment for communication and data sharing between sensors. In addition, dial-up communication was available so the subcontractor could check status of the system remotely. All trailers with the exception of the one farthest from the work zone area contained a Remote Traffic Microwave Sensor (RTMS) to detect traffic volume, vehicle speed, and lane occupancy. When occupancy thresholds were met, the sensor sent a message to the next trailer upstream and the flashing signs were activated. The signs stayed activated for a minimum of five minutes and direct drivers on where to merge. The trailer closest to the merge area was always activated. Michigan State Police were able to enforce the no-passing zone as needed by using a light on the back of each trailer; the light indicated when the sign was active and no passing allowed.
In addition to the DLM system, the Michigan DOT deployed several static message signs at highway entrance ramps and approaches to the merge area, as well as a dynamic message sign with the text, “MERGE LEFT,” and a visual arrow pointing to the left.
The Michigan DOT added specification for the DLM system components (trailers, signs, and microwave sensors) to the prime construction contract after award as a contract modification. The terms of the subcontract called out the leasing, installation and calibration, and maintenance of all ITS components (as needed). The prime contractor hired a subcontractor to design, install, calibrate, test, operate, and maintain the DLM system. The subcontract period of performance was for six months during each of two years at a total cost of $120,000. Each of the two six month periods included installation, test, and operation time. By leasing the system, the Michigan DOT was not required to perform equipment maintenance or store the systems after the construction project was completed. Furthermore, by leasing the systems, the Michigan DOT was able to take advantage of newer technologies as they became available.
The costs of the DLM system have dropped to $30,000 per deployment per direction. This cost includes furnishing the devices in operable condition, initial installation, operation, inspection, maintenance, cleaning, and removal at project completion.
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Initial costs to design, install, calibrate, test, operate, and maintain the DLM system: $120,000 Costs of the DLM system have dropped to $30,000 per deployment per direction.