Benefit

Advisory Variable Speed Limit System in Portland, Oregon reduces speed variation and the number of crashes in the area.

A frequent victim to severe congestion and inclement, unpredictable climate, Route 217 located southwest of downtown Portland receives relief from a variable speed limit system.


May 18, 2015
Portland,Oregon,United States


Summary Information

A Vehicle Advisory Speed (VAS) system was activated in summer 2014 on OR 217, a route which frequently suffers from high crash rates, severe recurrent bottlenecks, and highly unreliable travel times, as one component of the Oregon Department of Transportation’s (ODOT) OR 217 Active Traffic Management project. An evaluation was conducted to determine how effective the system was in improving safety and mobility on the route.

Methodology
  • Ten locations along OR 217 were fitted with large electronic variable speed message signs for both the northbound and southbound directions, with each travel lane having its own sign.
  • Data were analyzed using a "before" and "after" framework and were obtained from a diverse array of sources including freeway detectors, ODOT’s incident database, and the National Oceanic and Atmospheric Administration (NOAA).
  • Dual loop detectors in each lane recorded vehicle count, occupancy and speed measurements every 20 seconds. The weather-responsive component of OR 217’s VAS sign continuously collected real-time data from new RWIS sensors installed along the corridor. (Data from the RWIS sensors were not yet available so NOAA weather readings from nearby Hillsboro Airport were utilized for the analysis).
  • August through December of 2012 served as the "before" period for all traffic data analysis. The "after" period consisted of data collected from July 2014 – December 2014. Three years of crash data from the reported crash database, spanning from January 2010 through December 2012, was used as the "before" crash data set.

Findings
  • A more even split in flow across both lanes in each direction was recognized following the system's activation.
  • Travel time buffer indices largely fell for three of OR 217’s four primary lanes.
  • Overall speed variation during the PM peak fell by about 25 percent in each northbound lane.
  • In the northbound right lane, average travel times fell between 3 and 14 percent for all three daily segments. Mean travel times in the left lane increased an average of 8 to 10 percent during the peak hours and fell about 3 percent during midday hours.
  • The overall crash rate per million VMT increased 12.47 percent. However, the frequency of crashes in the immediate vicinity of the VSL signs decreased between 9 percent and 35 percent.

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Source

Evaluating the Effects of a Congestion and Weather Responsive Advisory Variable Speed Limit System in Portland, Oregon

Author: Matthew Downey (Portland State University)

Published By: Portland State University

Source Date: May 18, 2015

URL: http://pdxscholar.library.pdx.edu/cgi/viewcontent.cgi?article=3401&context=open_access_etds

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Goal Areas

Safety
Mobility

Typical Deployment Locations

Metropolitan Areas

Keywords

VSL, managed lanes

Benefit ID: 2016-01079