Marc Weaver, Deseret News
After several months of testing, UDOT will start using variable speed limit, or VSL signs, to remotely control the speed limit up and down Parleys Canyon during snowstorms. The speeds can be reduced to as low as 35 mph depending on weather, road conditions and motorists' speeds.

SALT LAKE CITY — With a series of snowstorms expected to hit northern Utah over the next week or so, the roads in Parleys Canyon could be a mess.

Beginning Wednesday, the Utah Department of Transportation will start using new variable speed limit signs up and down Parleys Canyon to help make the roadway safer for drivers.

“It’s an important corridor for us,” UDOT engineer Rob Miles said.

Nearly 50,000 vehicles travel through Parleys Canyon every day, according to UDOT.

When a storm hits the canyon, it can lead to treacherous driving conditions, and the posted speed limit is too fast for the conditions. The variable speed limit signs allow UDOT to remotely control the posted speed limit in 5 mph increments.

“We will take a look at roadway characteristics, surface temperatures, slickness of the roadway, what the storm is doing, and how drivers are reacting to the storm with their driving,” Miles said. "We will take all of that information back, analyze it, and a traffic engineer will post a new enforceable speed limit."

The normal posted speed limit is 65 mph through Parleys Canyon, but UDOT anticipates that during snowstorms the speeds could be as low as 35 mph.

“We believe the system will help us maintain a consistency of flow in the traffic,” Miles said. “The more consistent the flow, the safer people are going to be out there."

Sensors transmit the road conditions to UDOT, but motorists’ feedback also is critical. When vehicles slow down, engineers at the operation center know that drivers are reacting to deteriorating road conditions.

Speeds vehicles are traveling will be the primary factor in setting the variable speed limits, said Glenn Blackwelder, UDOT traffic operations engineer.

“If the majority of the drivers are telling us 50 seems comfortable, that’s where we are headed,” Blackwelder said.

The 15 signs — eight on eastbound I-80 and seven for westbound motorists — will warn drivers of unsafe conditions and tell them to slow down. UDOT has been testing the signs for several months. The system cost $750,000.

If it works well in Parleys Canyon, UDOT officials say they will consider it on other snowy roadways such as U.S. 89 in Sardine Canyon and U.S. 189 in Provo Canyon.

The signs can also be found on I-80 in Wyoming. The state of Washington uses them on a mountain interstate. A University of Washington study found that the system reduced the average vehicle speed by up to 13 percent and overall safety improved.