Capturing the Benefits of a Variable Advisory Speed System in Portland, Oregon: Empirical Before and After Evaluation

Abstract

The first variable advisory speed (VAS) system in Portland, Oregon, was recently installed on OR-217. This system, designed to be responsive to both congestion and weather, was installed to address issues along the corridor, including unreliable travel times, high crash rates, and substantial declines in performance during adverse weather. To assess the merits and effectiveness of the VAS system, a before and after analysis of corridor performance in terms of capacity, reliability, and safety is being conducted. This paper summarizes the findings of the before analysis and presents results from the after analysis during the first 9 months of operation. Before the system’s activation, OR-217 suffered from highly variable travel times, frequent severe bottlenecks, a high rate of rear-end collisions, and significant speed differentials between adjacent lanes. Though the system was activated in the summer of 2014 and the system’s long-term effects are not yet definitely established, some notable evidence of travel time reliability improvements has already been documented. The system’s safety impacts will be the subject of ongoing analysis.

Impact of Variable Speed Limit in a Connected Vehicle Environment on Truck Driver Behavior under Adverse Weather Conditions: Driving Simulator Study

“…In addition, it was found that the content of the warning message, such as warnings related to upcoming hazardous driving conditions, was helpful for improving driver compliance with the speed limit. Downey and Bertini made a before-after comparison study to investigate the benefits of variable advisory speed (VAS) system in Portland, Oregon ( 16 ). It was found that after 8 months of VAS operation, there have been notable improvements in travel time reliability as well as speed harmonization.…”