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Eastbound SR 520: Impacts of Freeway Surveillance and Control


The project entitled "Impacts of Freeway Surveillance and Control on Eastbound SR520", analyzed and evaluated the impacts of ramp metering and a new ramp HOV lane on eastbound SR520 which connects Seattle and the Eastside suburbs. Data analyzed included origin-destination surveys, manual vehicle occupancy counts, floating car travel-times, queue-length counts, electronic volume and lane-occupancy values, and bus travel-times. The results showed that the numbers of carpools and vanpools were significantly increased on the ramp with the new HOV lane and overall level-of-service was improved for mainline SR520. A significant number of trips were diverted from the local neighborhood to I-5. Queue-lengths and travel-times to the ramp mergers with the mainline increased significantly for both ramps. This was an expected result and had the desired effect of diverting trips from the neighborhood and increasing HOV ridership.


  • Date Published: February, 1987
  • Publication Number: WA-RD 99.1
  • Last Modified: August 23, 2007
  • Author: Nancy L. Nihan.
  • Originator: Washington State Transportation Center (TRAC)
  • # of Pages: 86 p., 1,610 KB (PDF)
  • Subject: Bus lanes, Carpools, Freeway operations, High occupancy vehicle lanes, High occupancy vehicles, Lane occupancy, Origin and destination, Queuing, Ramp metering, Ramps (Interchanges), Traffic lanes, Traffic volume, Transportation system management, Travel time, Vanpools, Vehicle occupancy.
  • Keywords: Freeway surveillance and control, transportation system management, ramp metering, high occupancy vehicle lanes, before-and-after studies, SR 520, Seattle.
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This abstract was last modified April 29, 2008