Variable Speed Signs (VSS) are used to report variable speed limits in certain areas. VSS allow operators to adjust (e.g., raise or lower) the posted speed limit without changing a physical sign. The signs may be used in conjunction with Intelligent Transportation Systems to adjust speed limits for several reasons including: congestion, construction, accidents, or weather conditions. As technology advances, the ease of use of VSS is also increasing. Reported speed limits may now be changed on the VSS remotely via email or telephone, at pre-set times of day, or manually. VSS also may be used to alter speed limits based on real time traffic, weather conditions, or construction.
For example, weather-related VSS may be used on roads where fog, ice, rain, snow, or other factors may influence safety. When weather conditions deteriorate to the point that hazardous conditions are impending, the operating agency may adjust (e.g., reduce) the speed limit to help minimize the likelihood of a traffic accident. Congestion-related VSS may be used when traffic volumes are building and congestion is likely. When volumes and/or speed exceed a predetermined threshold, an operational strategy may be deployed to handle more traffic volume at a reduced, but not stop-and-go, speed.
In the case of construction-related VSS, a long construction zone may often have actual construction occurring in only short segments of the zone. In addition, construction zones may be signed using static speed limit signs as if construction activity occurs throughout the entire day on each and every day. In reality, the intensity, duration, and location of construction activity may vary throughout the construction zone depending on the extent of work being performed. Providing more accurate and real time speed restrictions using VSS based on the level of construction activity may provide more accurate information to motorists and allow drivers to comply with the posted regulatory speed while improving safety in the construction zone. Adjusting (e.g., reducing) vehicle speed limits in active construction zones may improve safety for drivers and construction workers and may reduce the number and/or severity of accidents that occur in the zone.
Today's vehicles may have high definition cameras and advance radar systems that read the displayed value on a VSS from a long distance away. There are several shortcomings with relying on visual detection such as camera for VSS display value detection. For example, a vehicle's camera may confuse 50 km/h with 80 km/h. In some instances, the vehicle operator may be incorrectly warned, which may impede on the operator's safety.
Because municipalities (e.g., traffic management centers) that control the VSS may be unwilling to communicate the real time speed limits displayed on the VSS to third parties, there remains a continuing effort to provide improved systems and methods for reading a VSS with a highly assisting vehicle, predicting the posted speed limit value of the VSS, and calculating the confidence level of the predicted value.