In the right location, Variable Speed Limit signs can narrow speed differential and reduce crashes.
Wyoming has had success with placing a VSL signs on a 45 mile section of I-80 between Rawlins and Laramie. The signs are connected to an Intelligent Transportation System that feeds speed and weather data to Wyoming’s Transportation Management Center in Cheyenne. Other locations have used VSL signs, including Washington State’s Snoqualmie Pass on I-90, and have seen improved safety as well.
VSL signs allow engineers to monitor the traffic on the road, determine a speed that’s safer for conditions, and then change the posted speed on electronic signs. Engineers at UDOT’s Traffic Operations Center are preparing to evaluate I-80 through Parley’s Canyon as a location that may be appropriate for the signs.
Speed and fiber
Although all locations are different and need to be evaluated individually, like I-80 between Rawlins and Laramie, many of the crashes that do occur in Parley’s are due to high speeds and weather, explains engineer Scott Jones who will manage the operation of the VSL system for UDOT.
Conditions through the canyon can change quickly due to winter weather, and sometimes “in winter conditions, some people are not slowing down,” says Blaine Leonard, ITS Program Manager at UDOT. When some motorists slow down and others maintain high speeds, that differential “creates very unsafe conditions,” says Leonard.
WYDOT’s experience with the VSL sign system has shown that lowering the posted speed limit reduces the speed differential. Engineer Ken Schultz with WYDOT also reports that the department is seeing fewer crashes, fewer closures, and improved travel time reliability. Plans to expand the system to other locations in Wyoming are in the works.
Since VSL signs are part of an Intelligent Transportation System, “we need good fiber to connect to the signs and operate them efficiently,” says Leonard. Fiber optic cable buried along the freeway would allow the system to tie in with UDOT’s ITS system already in place.
UDOT is very early in the process of looking at placing the VSL signs, but indications are that the system may help improve safety through the canyon.