Utah Department of Transportation
A variable speed limit system in Utah’s Parley’s Canyon uses a combination of detection technologies, including SmartSensor HD, to continuously monitor traffic and environmental conditions to determine the safest speeds for drivers. Those speeds are posted in real time to variable speed limit signs and are immediately enforceable.
UDOT faced two significant challenges: environmental conditions and funding. First, Utah’s canyon roads can be treacherous during weather storms. Slippery roads and poor visibility contribute to unsafe driving conditions, which worsen when traffic becomes heavily congested.
Second, UDOT needed to be able to test variable speed limits without incurring additional costs. Variable speed limits, like many ITS applications, require a significant investment in detection technology, power, infrastructure and software. Avoiding these additional costs was key to the implementation of this system.
The Parley’s Canyon stretch of Interstate 80 east of Salt Lake City was selected as the test site because it met both criteria: it is heavily traveled and treacherous in winter; and much of the infrastructure required, including reliable power and previously installed sensors, was already in place.
The UDOT system uses a number of different technologies to monitor real-time conditions: SmartSensor HD monitors traffic speeds and volumes; environmental sensors measure road slickness, temperature and humidity; and traffic cameras monitor visibility. During snowstorms, traffic engineers will analyze the data provided by each sensor and determine the safest speed for drivers. Those speeds will immediately be displayed on variable speed limit signs located throughout the canyon.
“Instead of guessing, we can give drivers feedback about speed limits in storm events and minimize the likelihood of speeding,” says Chris Siavrakas, P.E., PTOE and project manager for UDOT.
“Instead of guessing, we can give drivers feedback about speed limits in storm events and minimize the likelihood of speeding.” –CHRIS SIAVRAKAS, P.E., PTOE AND PROJECT MANAGER FOR UDOT
UDOT conducted extensive research into variable speed limits and expects to see a reduction in weather-related traffic accidents. Because accurate traffic volumes and vehicle speeds are critical to the success of the system, SmartSensor HD is playing an important role in providing the data required. By reducing speeds to match real-time conditions, UDOT hopes to curb unsafe driving, canyon bottlenecks and vehicle slide-offs in order to create smoother, safer traffic flows. Other sites in Utah have been identified for variable speed limits should this pilot prove successful.
