March 15th, 2012

WYDOT SPEED STUDY

Uncategorized, by Catherine Higgins.

Variable Speed Limit Signs have helped reduce crashes on a 45 mile section of I-80 between Rawlins and Laramie in Wyoming.

I-80 in Wyoming -- wind and snow can cause low visibility and slick roads.

Photo courtesy Tom Kelly Photography. See the link below for more images.

Driving on the stretch of roadway can be treacherous when wind and snow combine to make for slick roads and poor visibility. “That’s our biggest challenge,” says Ken Schultz, WYDOT State Maintenance Engineer. To help motorists deal with road weather and improve safety, the Wyoming Department of Transportation studied the area and then placed speed VSL signs that can be changed according to conditions.

This WYDOT Traffic Camera photo shows I-80 between Laramie and Rawlins.

The signs, along with RWIS stations and speed detectors are connected to an intelligent transportation system that feeds data on speed and weather to Wyoming’s Transportation Management Center in Cheyenne. Online cameras let engineers and motorists see the conditions. Before speed is adjusted, engineers monitor traffic and weather to establish a pace speed more in line with conditions, and also consult WYDOT maintenance workers and highway patrol troopers in the area.

The protocol for reducing speed that uses weather, speed and experiential data has worked well,   says Schultz. “Everybody is really tuned in to it.” Speed sensors show that drivers are responding to the lowered speed on the VSL signs. Since the signs have been placed, fewer crashes have occurred. Schultz also believes that a switch to better de-icing chemicals have also played a role at improving safety.

While winter weather makes winter driving challenging, speed differential also contributes to unsafe conditions. When some vehicles are driving slowly and some are driving very fast, crashes are more likely to occur.

According to NCHRP Report 505, “studies show that regardless of the average speed on the highway, the more a vehicle deviates from the average speed, the greater its chances of becoming involved in a crash.”

Schultz believes the VSL signs, along with warning signs  and online cameras, have provided better information that “does help folks to make decisions about their travel,” including driving slower or even delaying travel until conditions improve.

UDOT is preparing to evaluate I-80 through Parley’s Canyon as a location that may be appropriate for VSL signs. 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 weather and speed differential.  

For more:

  • Read an article by Joan Barron of the Star-Tribune
  • See more photographs of I-80

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