The Queue Warning System (Stopped Traffic Advisory System) informs drivers of the presence of downstream stop-and-go traffic (based on real-time traffic detection) using warning signs and flashing lights. Drivers can anticipate emergency braking or slow down, avoid erratic behavior, and reduce queuing-related collisions. Changeable Message Signs (CMS) show a symbol or word when stop-and-go traffic is near. These systems are also referred to as “Congestion Warning,” “Stopped Traffic Warning System,” “Queue Warning,” “Be Prepared to Stop,” “Real Time Traffic Control System,” Work Zone Construction “Traffic Merge Warning System”, and “Smart Traffic Monitoring System”


  • Queue lengths are estimated to vary greatly, day-by-day and hour-by-hour, so a suitable location for the TTC advance-warning signage cannot be predicted. Note: Signs placed over a mile ahead of confirmation are typically forgotten by the motorist.
  • Queue lengths may encroach upstream beyond a motorist’s reasonable expectations for stopped traffic, and there is probability that the geometrics (terrain) may cause poor visibility of end-of-traffic queues, causing short reaction times and panic stopping.
  • Queues initiated on crossroads are estimated to cause traffic conflicts and/or delays on the mainline road, such as back-ups beyond the length of ramps, through or around turns in intersections, or other hazardous congestion situations.


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stopped or slowed traffic when flashing    real time traffic control system     traffic merge warning system




Queue Warning System can help reduce primary and secondary crashes by alerting drivers to congested conditions. Incident severity is reduced because drivers are prepared for impending congestion. Stopped Traffic Advisory Systems can also help delay the onset of congestion. With more uniform speeds, traffic flows more smoothly and efficiently.


Deployment criteria and anticipated effects are suggestions that were provided by the MnDOT 2007/2008 report “Minnesota Intelligent Work Zone Toolbox.”

TxDOT Study: Innovative End-of-Queue Warning System Reduces Crashes Up to 45%