Before-After Analysis of Safety Effects of Variable Speed Limit System Using Full Bayesian Models

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 Seattle, United States since 2010. A Full Bayesian (FB) before-after analysis was conducted based on 9,787 crashes that occurred in a 72-month study period. The analysis was conducted for all crashes, crash severity levels, crash types and crash causes. The FB before-after results implied that the total crash count was reduced by 32.3% with a standard deviation of 3.58% after the implementation of VSL system on the target freeway. The decrease in number of no injury crashes is greater than the decrease in crashes with severe injury and possible injury. The effect with respect to reducing head-on, face and leading-end crashes was with the most beneficial among all crash types, while the effect on rear-end crash was the least. The study also compared the traffic speed features in the before and after periods in order to fully evaluate the impacts of the VSL system on traffic operations. The result indicated that, the difference in speed was apparently reduced with the VSL system deployed The results of this study are particularly valuable for policy making and cost-benefit evaluation associated with VSL system implementations.

• Supplemental Notes:
  • This paper was sponsored by TRB committee ANB20 Standing Committee on Safety Data, Analysis and Evaluation.
• Corporate Authors:

  Transportation Research Board

  ,    
• Authors:
  • Pu, Ziyuan
  • Guo, Xiaoyu
  • Li, Zhibin
  • Jiang, Ying
  • Wang, Yinhai
  • Zhang, Chao
• Conference:
  • Transportation Research Board 98th Annual Meeting
  • Location: Washington DC, United States
  • Date: 2019-1-13 to 2019-1-17
• Date: 2019

Language

• English

Media Info

• Media Type: Digital/other
• Features: Figures; References; Tables;
• Pagination: 6p

Subject/Index Terms

• TRT Terms: Bayes' theorem; Crash causes; Crash severity; Crash types; Highway safety; Variable speed limits
• Geographic Terms: Seattle (Washington)
• Subject Areas: Data and Information Technology; Highways; Safety and Human Factors;

Filing Info

• Accession Number: 01698130
• Record Type: Publication
• Report/Paper Numbers: 19-03134
• Files: TRIS, TRB, ATRI
• Created Date: Mar 1 2019 3:51PM