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Evaluation of Variable Speed Limit/Variable Advisory Speed Systems

Project #: 4W4594
Start Date: 09/05/2013
End Date: 07/31/2016
Status: Completed

Freeway congestion leads to mobility delays, wasted fuel, reduced safety and air quality impacts. Weather conditions also cause delays and increase the potential for crashes.  Active Traffic Management (ATM) systems such as Variable Speed Limit (VSL) and Variable Advisory Speeds (VAS) provide traffic and weather responsive guidance to drivers and have shown promise for reducing congestion and weather-related crashes by reducing drivers’ speeds.


The Oregon Department of Transportation is currently implementing ATM, VSL, and VAS systems on state highways. Evaluating the performance of initial systems will be vital for determining how and where to implement similar systems around the state. This project will evaluate the performance of two systems:

  • The OR 217 installation project is on a congested 7 mile segment of urban highway in the Portland area. The project includes a weather-responsive VAS, posting of real-time travel times, queue warning, infrared and laser weather detection sensors, and a weather-responsive curve warning system.
  • The US26/OR 35 Mount Hood Safety and Traveler Information Project covers 67 miles of rural highway. It includes VSL, VAS, a variable message sign (VMS), and a Road Weather Information System.


This project will collect before and after data to evaluate the system’s impact on speed, crash occurrence, traveler experience, driver behavior and other factors. The findings will be used to produce lessons learned and implementation guidance for future project deployments.



The objective of this project is to evaluate the performance of variable speed limit (VSL) and variable advisory speed (VAS) systems in urban (OR 217) and rural (US26/OR35) settings in Oregon and provide guidance for future implementations of similar systems. The research will examine the before and after performance data of the VSL/VAS systems in addressing congestion, travel times, weather information, and crashes based on the specific issues of each corridor.


  • Ahmed Al Kaisy
    Ahmed Al Kaisy
  • David Veneziano
    David Veneziano