An innovative end-of-queue warning system was implemented on a 96-mile section of Interstate 35 (I-35) in central Texas as part of a freeway widening project.  In general, the system was designed to alert motorists of slowed or stopped vehicles ahead of them as they approached active construction projects on I-35. These work zones required lane closures and merging at nighttime in rural areas where drivers would not expect sudden slowdowns.

The system used portable roadside radar detection devices mounted upstream of work zones and lane closures to monitor and measure the speeds of approaching vehicles. An algorithm was used to analyze the detector data and select a warning message on portable roadside dynamic message signs installed further upstream. The expected volume and capacity reduction from a work zone database were used to estimate the maximum expected queue for the night in order to guide placement of the sign. The warning message informed drivers of the work zone and approximate distance to the slowed or stopped traffic, enabling traffic to gradually reduce speed as they approached the end of a vehicle queue.