Study Found the Display of Queue Warning Messages Decreased the Number of Crashes by 12 to 56 Percent.
Synthesis Report Evaluating Safety Impacts and Deployment Practices of Queue Detection and Warning Systems in Minnesota, Pennsylvania, Texas.
Nationwide, United States
Traffic Management Systems Actively Managing the Display of Queue Warning Messages
Summary Information
Freeway congestion often leads to sudden slowdowns and rear-end crashes, especially when drivers encounter unexpected queues. To reduce these risks, traffic management systems (TMS) use real-time data from sensors and other monitoring tools to detect unstable traffic conditions and display warning messages on digital road signs before drivers reach slow or stopped vehicles. By improving how traffic warnings are managed and displayed, these systems enhance roadway safety, support smoother travel through work zones or bottlenecks, and complement other smart traffic management strategies such as variable speed limits and lane-use control. This study reviewed and showcased the benefits of the current TMS nationwide, including Minnesota, Pennsylvania, and Texas State DOTs.
METHODOLOGY
This report synthesizes results from prior State DOT evaluations and agency deployments and summarizes common assessment considerations, data sources, and operational practices for implementing queue warning message strategies. It began with an assessment of existing monitoring tools, including sensors, cameras, and message signs, to determine whether they could reliably detect slowdowns and warn drivers. The evaluation also identified which data sources, such as roadway sensors or vehicle probe data, were most useful for tracking congestion. Teams then refined algorithms to detect forming queues and select appropriate messages, adding software or procedures when needed to manage automated alerts. This study focused on quantifiable safety benefits to evaluate the effectiveness of TMS deployment in Minnesota, Pennsylvania, and Texas.
FINDINGS
- In Minnesota, there was a 56 percent reduction in crashes and a 69 percent reduction in near-crashes as a result of posting queue warning messages along westbound I-94 near I-35W in Minneapolis. (Note: MnDOT cautioned that the estimated crash reductions may be overstated and may apply only to a specific crash type and time period.)
- The Pennsylvania Department of Transportation found that using queue warning messages in work zones along a 40-mile section of I-78 reduced overall crashes by 12 percent and lowered injury and fatal crashes by 23 percent.
- The Texas Department of Transportation discovered that combining queue warning messages with portable rumble strips placed ahead of nighttime work-zone lane closures on I-35 in Central Texas reduced crashes by 44 percent compared with conditions where no warnings were displayed.
