Safety Evaluation of Minnesota’s Queue Warning System Implemented on Interstate-94.
Minneapolis, Minnesota, United States
Evaluation and Refinement of Minnesota Queue Warning Systems
Summary Information
Queue Warning systems make use of a variety of detection systems and algorithms and can be used to inform drivers of crash prone conditions. This project utilized the extensive surveillance and data collection activities carried out between June 2016 and August 2018 for evaluating Minnesota DOT’s 2017 queue warning development and deployment project (MN-QWARN) that was implemented in the right lane of a 1.7-mile-long freeway segment of Westbound Interstate 94 (I-94 WB) near downtown Minneapolis, MN. In order to evaluate the transferability of the MN-QWARN system, the researchers deployed the system at an additional site between October 2020 and June 2022 that was approximately 0.75 miles upstream from the original site. The deployment included two new installed MTO traffic detection and monitoring stations, a changeable message sign at the far upstream end of the corridor, and a MNDOT vehicle speed detector reporting 30-second average vehicle speed data on three lanes of the road.
METHODOLOGY
The MN-QWARN system relies on the assumption that only some of the slow-and-go conditions on the road are dangerous. Instead of warning drivers of any slow traffic ahead, the MN-QWARN algorithm focuses on quickly moving shockwaves which typically affect only a small number of vehicles and can be especially dangerous for distracted drivers. These waves move the fastest when there is slow moving traffic downstream and when there is high speed and high-density traffic upstream. The MN-QWARN collects and passes the detection data to a crash-probability model to assess the likelihood of a crash. Based on this crash probability, the algorithm determines if a warning message should be generated by comparing the crash probability with preset thresholds and real-time traffic conditions. The system also includes several overrides as part of the deployment on the preexisting MnDOT changeable message sign. The congestion override also prevents the sign from being turned on to reduce driver overexposure to the warning by not displaying a warning when drivers are already travelling slowly. To evaluate the effectiveness of the re-deployment of the MN-QWARN system, the researchers utilized Minnesota Crash Mapping Analysis Tool (MnCMAT2) to obtain crash records for the deployment site for 2019 (pre activation) and 2021-2022 (post-Covid with system activated.)
FINDINGS
- For the original site, the analysis of substantial data from its two-year operational period (2016-2018) indicated that the system had not only sustained the 22 percent reduction in crashes from the initial three-month evaluation period but had also further decreased crashes and near-crashes. Specifically, crashes were reduced by 56 percent and near-crashes saw a 69 percent reduction.
- The re-deployment results highlighted transferability in the queue detection model with a detection rate up to 64 percent and false alarm rate as low as 23 percent.
