Collisions on I-5 in Washington State have been reduced by 65-75 percent in a 7.5 mile corridor where an active traffic management system was deployed.
Results from WSDOT's 2010 Congestion Report.
Made Public Date


United States

The Congestion Report Gray Notebook Special Edition WSDOT’s comprehensive analysis of system performance on state highways,

Summary Information

Washington State DOT (WSDOT) produces an annual report called The Gray Notebook, in order to evaluate their performance measurements for their highway system. The 2010 Congestion Report focuses on data comparisons between 2007 and 2009 highway capacity, usage and delay statistics. WSDOT worked to improve the operational efficiency of Washington's highways through ITS deployments such as variable speed limits, dynamic message signs, high occupancy tolling (HOT) lanes, and incident response teams, as well as through strategic expansion of roadways at reoccurring bottlenecks. The authors note that some of their findings may have been impacted slightly by the annual VMT per capita decrease of 300 miles (1.6 percent) between 2007 and 2009, a likely result of the recession and high gasoline prices.

WSDOT deployed a series of 15 sign bridges every half-mile over a 7.5 mile stretch of I-5 between Boeing Access Road and I-90 in Seattle. These sign bridges hold dynamic message signs, which display variable speed limits, lane closures, merge areas and traveler information. WSDOT deployed these Smarter Highways gantries in order to reduce traffic speeds as vehicles approach the site of an incident or construction in order to avoid "panic breaking" by drivers as they approach incidents or construction and therefore theoretically reduce collisions (both secondary and primary). The variable speeds are calculated by an algorithm with live traffic data inputs.

While WSDOT admits that it is too early to judge the effects of installing Smarter Highways gantries on the number of collisions and congestion (as only 3.5 months of data were collected before the report was written), there were only 35 collisions between August 10 and November 1, 2010. During the 5 previous years during the same period, the number of collisions ranged from 100 to 140. Post deployment collisions were between a quarter and a third of their previous levels.