A Pilot Application of the Sliding Window Screening Method on Virginia Roadways

About the report:

This study evaluated the practicality and efficacy of implementing the sliding window screening method recommended in the Highway Safety Manual for systemically identifying high-risk segments in the Virginia roadway network.  The current simple ranking method used by the Virginia Department of Transportation (VDOT) to identify high-risk segments has inherent limitations due to the effect of segment length variations, and the sliding window screening method allows segments to be compared on a consistent length basis.  The study proposes a homogeneous segmentation network that maintains consistency in segment characteristics based on annual average daily traffic and type of safety performance function.  

In this study, the sliding window screening method, executed in Python, was applied to the newly generated homogeneous segments.  The evaluation of the performance of this method encompassed multiple aspects, including an assessment of potential for safety improvement (PSI) values, segment rankings, and comparison of results with the current VDOT PSI list.  Further, the study investigated the sensitivity of window size selection to the inherent stochastic nature of crash occurrences.  Specifically, smaller window sizes were more effective in identifying localized crash “hotspots,” and larger window sizes delivered a more general overview of the entire segment.  The study also advises against the use of a single year’s ranking for determining high-risk PSI segments, owing to this stochastic variation.   

The study found that the sliding window screening method does not have inherent bias toward two roadway attributes: segment length and median presence.  This finding mitigates the existing segment length variation problem in the current approach.  The study concludes that the sliding window screening method holds promise in enhancing current practices employing the simple ranking method.   

The study recommends that VDOT consider deploying the new segmentation network and adopting the sliding window screening method for the computation of PSI values on a statewide basis to enhance the effectiveness of network screening processes. 

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