Although PTMS solutions have been widely deployed, systems using advance machine vision queue detection algorithms are still being explored. This study evaluated the technical performance of a prototype system and provided lessons learned.
Three sites in Minnesota were equipped. Two signal controlled intersection sites and one highway construction site. The algorithm was calibrated at each site and then video components of the system were used to evaluate performance.
Site 1 Description
The first site was an intersection located west of SH-100, at the crossing of Glenwood Avenue and SH-55. The camera was tilted down 20 degrees from horizontal, with a height of 28 feet above the roadway to provide a clear view of traffic well beyond 500 feet from the intersection.
Site 2 Description
The second site was an intersection at Rhode Island Avenue and SH-55. This site allowed for testing significant cross-lane view angles from an off-shoulder location covering three lanes of traffic. At this site, the camera was tilted down 30 degrees from horizontal, with a height of 28 feet above the roadway to provide a view of traffic just beyond 500 feet from the intersection.
Site 3 Description
The third site was located north of the Broadway Avenue Intersection along SH-280 at a work zone site with temporary traffic control measures in place. The taper zone was approximately 1000 feet. The system was deployed for 10 days at this location.
The following were recommended to ensure good system performance:
- Ensure machine vision systems accurately detect the onset of a queue. Align the camera azimuth angle with the roadway as much as possible, with respect to the location of the stop bar, even if this necessitates a reduction in the queue length detection area.
- Ensure the stop bar is visible. A stop bar must be completely visible and projected horizontally across all lanes to be monitored.
- Consider the potential for cross-lane occlusions. Monitoring more than two lanes can be problematic if the system is deployed at a lateral distance of greater than one lane from the lane edge.
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