In Minneapolis, implementation of a queue warning system resulted in 54 percent decrease in near-crashes and 22 percent decrease in crashes along segment of interstate.

The queue warning system (QWARN) uses in-pavement loop detectors and Machine Vision Detectors (MVDs) to sense dangerous traffic conditions and delivers warning messages to drivers to increase alertness

June 13, 2017
Minneapolis; Michigan; United States

Summary Information

The Minnesota Traffic Observatory, with the support of the Minnesota Department of Transportation (MnDOT), developed a system to identify traffic shockwaves and queues that used existing intelligent lane control signals (ILCS) to warn motorists upstream. When potentially unsafe traffic conditions were detected, the ILCS would display warning messages to travelers, who would then adjust their driving accordingly. The project's goals were to both design a system that was as accurate as possible in its detection methods and to communicate with drivers in a way that maximized their attention levels. The system was field-tested from May to August of 2016 on a segment of I-94 between Minneapolis and Saint Paul that was known to have a high frequency of rear-end collisions.

As part of the study, the University of Michigan developed a second system, for deployment along a segment of I-35W that was also known for its rate of rear-end collisions. This second system was based on an estimation of freeway queue length. Evaluation of this method was not as thorough as it was for the prior system, though it was broadly indicated to have resulted in a reduction in speed variance near queues and a general normalization of speed between upstream and downstream locations.

  • Prior to installation, based on 2013 data, there were 11.9 crashes per million vehicle miles of travel (MVMT) and 111.8 near-crashes per MVMT.
  • In the three months of deployment, event frequency reduced to 9.34 crashes per MVMT and 51.8 near-crashes per MVMT.
This indicates a 22 percent decrease in crashes and a 54 percent decrease in near-crashes during the pilot period.

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Development of a Queue Warning System Utilizing ATM Infrastructure System Development and Field Testing

Author: Hourdos, John et al.

Published By: Minnesota Local Road Research Board, Minnesota Department of Transportation

Source Date: June 13, 2017



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Typical Deployment Locations

Metropolitan Areas


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Benefit ID: 2018-01275