A variable speed limit system consisting of multiple ITS components and covering 40 miles over the Snoqualmie Pass in Washington was designed and implemented for $5 million.

From the Rural ITS Toolbox report: Subsection 7.1 Speed Warning Systems (Travel Aid)

November 2001
Seattle; Washington; United States

Summary Information

The Washington State Department of Transportation (WSDOT) deployed a variable speed limit (VSL) system to improve safety and reduce winter-weather related accidents on a 40-mile stretch of I-90 over the Snoqualmie Pass. The system consists of radar detection, six weather stations, nine variable message signs (VMS), and radio and microwave transmission systems. The weather stations monitor temperature, wind, humidity, precipitation and road surface conditions. Current traffic speed and weather condition data are collected and transmitted by packet radio and microwave communication to the Travel Aid control center. The system calculates safe speeds which are confirmed by WSDOT staff and transmitted to the dynamic message signs deployed along Snoqualmie Pass. The variable message signs were installed on the mainline downstream of each on-ramp, and the signs displayed either the maximum legal speed limit, or an enforceable reduced speed limit when conditions warranted. Pass conditions are also posted to the WSDOT website. Travel Aid cost $5 million to design and implement. The system has been in operation beginning winter 1997-98.

Each of the nine variable message signs in the test area was formatted to display the speed limit on the left hand side of the sign and a three-line message (ten characters per line) on the right. Four additional variable message signs were installed outside the test area; however, these signs did not post speed limits and were formatted to use all 15 characters per line for traveler information on roadway conditions, tire chain requirements, and road closures.

Speed limits were changed in 10 mph increments. If traction tires were advised, the speed limit was reduced to 55 mph; if traction tires were required, the speed limit was reduced to 45 mph; and if chains were required, the speed limit was reduced to 35 mph.

See Also:

Robinson. "Examples of Variable Speed Limit Applications." Presentation given at the Speed Management Workshop held in conjunction with the 79th Annual Meeting of the Transportation Research Board. January 2000.

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Rural ITS Toolbox

Author: Deeter, D., H. M. Zarean, and D. Register

Published By: U.S. DOT Federal Highway Administration

Source Date: November 2001

EDL Number: 13477

Other Reference Number: FHWA-OP-01-030

System Cost

Design and implementation cost: $5 million (1997).


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Costs From This Source

A bicycle safety system was installed for $5,000 at a tunnel near Chelan, Washington.

A Minnesota integrated communications system project to share application of ITS across transportation, public safety, and transit agencies cost just over $1.5 million.

A pedestrian safety system was deployed in downtown Boulder, Colorado; total project cost ranged from $8,000 to $16,000.

A variable speed limit system consisting of multiple ITS components and covering 40 miles over the Snoqualmie Pass in Washington was designed and implemented for $5 million.

Animal warning system deployed in the Greater Yellowstone Rural Intelligent Transportation Systems (GYRITS) corridor at a cost of $3,800 per site.

Colorado DOT deployed a truck speed warning system in Glenwood Canyon at a cost ranging from $25,000 to $30,000.

During a pilot project Minnesota State Patrol vehicles were equipped with an accident investigation system at a cost of $8,000 to $10,000 per vehicle.

Emergency preemption equipment was deployed at several intersections in British Columbia, Canada at a cost of $4,000 (Canadian) per intersection.

The cost to equip a police vehicle in Dane County, Wisconsin for coordinated interagency incident response was $8,000 to $10,000.

Benefits From This Source

In Colorado, a downhill truck speed warning system installed on a curved section of I-70 reduced 85th percentile truck speeds by 27 percent.

Lessons From This Source

Provide traveler information in rural areas to allow for good travel decisions in inclement weather and construction season.

Use speed warning signs on dangerous curves to reduce speeds of trucks.

Cost ID: 2003-00015