Before–After Safety Evaluation of Coordinated Ramp Metering System Using Empirical Bayes Approach: A Case Study on I-80 in California
Publication: Journal of Transportation Engineering, Part A: Systems
Volume 149, Issue 11
Abstract
Coordinated ramp metering (CRM) systems are implemented on freeways primarily to improve operational conditions. However, smoother traffic flow resulting from CRM may also have significant safety benefits. The main objective of this research is to evaluate the safety performance of CRM systems on the Interstate 80 (I-80) corridor in California by using an empirical Bayes before–after approach. We collected geometric features, traffic volume, and historical crash data from I-80 in the San Francisco Bay area (Caltrans District 4). Then, the freeway safety prediction methodology implemented using the Enhanced Interchange Safety Analysis Tool (ISATe, developed as part of a National Cooperative Highway Research Program Project 17-45) was utilized to estimate the counterfactual, i.e., the number of crashes if no CRM system was implemented on the corridor. Based on a comparison of this counterfactual with the actual crash counts in the post-CRM period, CRM implementation led to a decrease in the number of fatal and injury crashes on I-80 but an increase in minor property damage only crashes. Disaggregate analysis of the results was used to gain further understanding of the CRM safety performance. The differences in the resulting safety performances were contextualized based on the different settings where the systems were implemented. As expected, CRM systems were more effective for segments in the vicinity of ramps. Safety performance functions for shorter durations (e.g., for peak hours), the subject of the ongoing National Cooperative Highway Research Program Project 22-48, will help more precisely estimate the safety impact of CRMs.
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Data Availability Statement
Some data and models that support the findings of this study are available from the corresponding author upon reasonable request.
Acknowledgments
The research team wishes to acknowledge the California Department of Transportation (Caltrans) and Mineta Transportation Institute (MTI) for the financial support in this research as part of project MTI Project #1812 (Caltrans Task Order 3506). Caltrans District 4 also provided the data used herein. The efficiency analysis for this study was first conceived as part of a project funded by UTC consortium C-TEDD (Center for Transportation Equity Decisions and Dollars). Dr. Srinivas Geedipally of Texas Transportation Institute provided valuable guidance on the use of the ISATe tool.
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Information
Published In
Journal of Transportation Engineering, Part A: Systems
Volume 149 • Issue 11 • November 2023
Copyright
© 2023 American Society of Civil Engineers.
History
Received: Dec 21, 2021
Accepted: Feb 3, 2023
Published online: Aug 22, 2023
Published in print: Nov 1, 2023
Discussion open until: Jan 22, 2024
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