Study Details

Study Title: Evaluating Safety Effects of Variable Speed Limit System using Empirical Bayesian Before-After Analysis

Authors: Pu et al.

Publication Date: JAN, 2017

Abstract: Variable speed limits (VSL) have been increasingly used to improve traffic safety on freeway mainlines. The primary objective of this study was to evaluate the safety impacts of the VSL system implemented on Interstate 5 in Washington since 2010. An observational Empirical Bayesian (EB) before-after analysis was conducted based on 9787 crashes that occurred in the 72-month period. The analysis was conducted for all crashes, and crash severity levels. The EB before-after result implied that the total crash count was reduced by 29% with a standard deviation of 5% after the VSL system was applied in Washington. The counts of crashes with no injury and possible injury decreased more than crashes with severe injuries. The evaluation results of this study are particularly valuable for policy making associated with VSL system implementation projects.

Study Citation: Pu, Z., Z. Li., W. Zhu, Z. Cui, and Y. Wang. "Evaluating Safety Effects of Variable Speed Limit System using Empirical Bayesian Before-After Analysis". Presented at the 96th Annual Meeting of the Transportation Research Board, Paper No. 17-05863, Washington, D.C., (2017).


CMFs Associated With This Study

Category: Advanced technology and ITS

Countermeasure: Install Variable Speed Limits

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.71 29 4 Stars All All Principal Arterial Interstate Urban
0.75 25 4 Stars All O Principal Arterial Interstate Urban
0.72 28 4 Stars All Principal Arterial Interstate Urban
0.81 19 2 Stars All Principal Arterial Interstate Urban