FHWA published guidance on the use of ITS in rural locations referred to as the Rural ITS Toolbox. The document represents best practices at the time of publication with regard to many ITS services including Emergency services, Tourism & Traveler Information, Traffic Management, Rural Transit, Crash Prevention, Operations and Maintenance, and Surface Transportation & Weather.
One such best practice is speed warning systems, a tool available for crash prevention and safety. Speed warning systems are effective for locations that experience sizeable speed differentials such as mountain passes or curves that require commercial vehicles to slow more than passenger vehicles. Typical speed warning systems are composed of speed measurement technology, an automatic speed classification system, a weigh-in-motion system, and a dynamic message sign to communicate with drivers. The primary use for this technology is for commercial vehicle operations.
In Glenwood Canyon, Colorado a truck speed warning system was installed in September 1996 to improve safety and reduce runaway truck accidents on a steep section of I-70. The automated system used a radar gun to determine the speed of trucks approaching the curve, and if a speeding truck was detected a dynamic message sign was activated that read "YOU ARE SPEEDING AT [XX] MPH / 45 MPH CURVE AHEAD." The curve, was located on a down grade and curve geometry tightened from 7 to 5 degrees midway. Based on limited sight distance, the maximum design speed for the curve was estimated at 45 mi/h.
Speed studies conducted before and after the system was activated indicated that the warning system reduced 85th percentile truck speeds from 66 to 48 mi/h, a 27 percent reduction.
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