Keeping traffic moving
Seattle has become the second U.S. city to implement an active traffic management (ATM) system, employing approaches that have been tried and tested in several European countries. The resulting "smarter highway" features integrated technologies that communicate with drivers to help manage traffic in chronically congested areas and improve roadway safety.
The Washington State Department of Transportation (WSDOT) installed the ATM system along a 7-mile stretch of Interstate 5, a major artery traversing the southern part of Seattle. Parsons Brinckerhoff developed the system concepts and conceptual design with WSDOT.
Based on real-time road conditions, the system reduces traffic speeds upstream of congested areas and advises motorists to merge into another lane to avoid a blocked lane caused by an accident scene, stalled vehicle or work zone. Gantries over each lane display changing speed limits and lane control symbols. Activation of the variable speed limit signs alerts motorists that they are approaching congestion, collisions or backups, and advises them to slow down. Gantries are installed approximately one-half mile apart so at least one gantry is visible to drivers at all times.
The system also includes side-mount and overhead variable message signs that alert travelers about traffic conditions ahead. Signs displaying estimated travel times and other traffic conditions allow drivers to make on-the-road route decisions.
WSDOT added roadway traffic sensors and cameras, and installed fiber-optic cables to feed data into the traffic management center that controls the signs. Data input is monitored 24/7 by traffic engineers, and an engineer verifies the information before the system is activated.
Early evidence suggests that the system is accomplishing its primary goal of collision reduction. A total of 35 crashes occurred within the installation area between Aug. 10 and Nov. 1, 2010. For the past five years, collisions during the same timeframe ranged from 100 to 140. WSDOT implemented a similar system on SR 520 on Nov. 16, 2010, and plans to construct another ATM system on I-90 in the first half of 2011.
Project: Active Traffic Management
Jurisdiction: Washington State
Agency: Washington State Department of Transportation
Conceptual design: New York-based Parsons Brinckerhoff
RFP preparation/Pre-design: Pasadena, Calif.-based Jacobs Engineering
Design/builder: Everett, Wash.-based Elcon Corp.
Date opened: Aug. 10, 2010
Construction cost: $21 million
