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)
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.
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. http://safety.fhwa.dot.gov/speedmgt/vslimits/
Puget Sound Regional Council. Smart Trek Website. http://www.psrc.org
“Variable Speed Limit and In-Vehicle Signing Operational Test” available at http://ntl.bts.gov/lib/jpodocs/briefing/12164.pdf
Click here for a picture of a Travel Aid speed warning sign.
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-01-030URL: http://ntl.bts.gov/lib/jpodocs/repts_te/13477.html
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Intelligent Transportation Systems > Road Weather Management > Information Dissemination > Dynamic Message Signs
Intelligent Transportation Systems > Road Weather Management > Traffic Control > Variable Speed Limits
Intelligent Transportation Systems > Freeway Management > Lane Management > Variable Speed Limits
DMS, CMS, VMS, Changeable Message Signs, Variable Message Signs, VSL, managed lanes