UDOT

The UDOT Traffic Operations Center (TOC) has a tool to enhance safety for drivers  on I-80 – one of the most heavily-traveled roads in the state. On Jan. 8, 2014, 15 new variable speed limit (VSL) signs were activated along I-80 in Parley’s Canyon. The signs are controlled by the TOC to help maintain consistent traffic flows and assist drivers in adjusting speeds when necessary due to weather conditions.

The 15 signs – 8 eastbound and 7 westbound, located between the mouth of the canyon and Jeremy Ranch, are equipped with LED display screens that allow UDOT to remotely adjust speeds. These adjustments will be made based on driver behavior and road conditions.

“We are always looking for technologies to help us manage traffic more effectively and enhance safety,” said UDOT Region Two East District Engineer Robert Miles. “These signs will help keep drivers moving and reduce the number of weather-related crashes in Parley’s Canyon.”

The variable speed limit signs in Parley’s Canyon have been divided into four zones – an eastbound lower zone and westbound lower zone, from the mouth of the canyon to Mountain Dell/Lambs Canyon, and an eastbound upper zone and westbound upper zone, from Mountain Dell/Lambs Canyon to Kimball Junction. When a speed limit is adjusted for a specific zone, the new speed limit will be displayed on all signs within the same zone. These zones were created because of the differences in weather patterns and average speeds observed in the canyon due to changes in elevation.

The TOC will monitor speed limits in the canyon. In the event of poor weather or low visibility, a traffic engineer will be able to review information such as current road conditions, weather forecasts, snowfall rates, observed speeds, and reports from maintenance personnel. Based on this information, the engineer can make the decision to reduce the speed limit as needed. Depending on conditions, speed limits may range from 35 to 65 miles per hour.

The Parley’s variable speed limit signs were the first of their kind in Utah. Other states, including Washington, Wyoming, Colorado and Nevada, also used these signs and observed a reduction in weather-related crashes in areas where these signs were employed. Washington (Snoqualmie Pass – I-90) and Wyoming (east of Evanston – I-80) in particular use these signs in areas similar to Parley’s Canyon: interstate highways with moderate to heavy traffic, with significant elevation differences, that are prone to inclement weather.

The Parley’s Canyon VSL project was developed jointly by UDOT and the Utah Highway Patrol (UHP). The speed limits posted on these signs are not merely advisory speeds, but regulatory speed limits that will be enforced by UHP troopers.

I-80 in Parley’s Canyon was selected as the location for this project due to its changing weather conditions, heavy traffic, and existing fiber optic communications network. The investment for the design and construction for the new signs was $750,000, and the annual operating expense is estimated between $7,500 and $10,000. UDOT is also considering installing variable speed limit signs in other locations around the state, such as Sardine Canyon and Provo Canyon, based on the results of this project.