Project Benefits
- More Accurate Queue Length Measurement
- Increased Ramp Metering Effectiveness
- Higher Freeway Throughput, Reduced Travel Time and Reduced Crashes
Project Team
- USDOT
- Mn/DOT
- SRF Consulting Group, Inc.
- Sensys Networks Inc. (Brown Traffic Products, Inc.)
- Wavetronix LLC (Traffic Control Corporation)
Project Documents
Ramp Queue Detection
Project Description
Several freeway on-ramps throughout the Metro area have unique geometries, such as a wide roadway section at the top of the ramp, that make it difficult for standard loop counting systems to accurately count all vehicles. Over the course of a peak period, these counting errors can add up, resulting in inaccurate queue length estimates. Because of this, Mn/DOT makes conservative estimates so that vehicles do not have to wait in the queue for over four minutes. This adversely affects mainline capacity during peak hours. The Ramp Queue Detection Project has developed and tested innovative detection systems to overcome this problem.
The focus of the project was on three systems for detection. The first system involves in-pavement magnetic sensors installed along the length of the ramp. Based on which sensors report stopped vehicles, the queue can be estimated. A second system involves sensors installed upstream or downstream of the ramp to directly “view” the queue length using a detector. The final system evaluated is a side-fire sensor that is located adjacent to the entrance ramp. As vehicles enter the ramp, they are counted regardless of the lane of travel.