Study Details

Study Title: Before-After Safety Evaluation of Coordinated Ramp Metering System using Empirical Bayes Approach: A Case Study on I-80 in California

Authors: Amirarsalan Mehrara Molan, Anurag Pande, and Stuart Madison Harvey

Publication Date: 2022

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 I-80 corridor in California using an empirical Bayes (EB) before-after approach. The authors collected geometric features, traffic volume, and historical crash data from I-80 in the San Francisco Bay area (Caltrans District 4). Then, the Enhanced Interchange Safety Analysis Tool (ISATe; developed as part of a National Cooperative Highway Research Program project) was utilized to predict the counterfactual, i.e., the number of crashes if no CRM system was implemented on the corridor. Based on the results, CRM implementation has led to a decrease in the number of fatal and injury crashes on I-80. Spatial analysis of the results is used to gain further understanding of the CRM safety performance. The differences in the resulting safety performances are contextualized based on the differences in settings where the systems are implemented. As expected, CRM systems are more effective for segments in the vicinity of ramps. Safety Performance Functions (SPFs) for shorter durations (e.g., for peak hour), the subject of an ongoing NCHRP project, will help in more precisely estimating the safety impact of CRMs.

Study Citation: Molan, A. M., Pande, A., and Harvey, S. M. “Before-After Safety Evaluation of Coordinated Ramp Metering System using Empirical Bayes Approach: A Case Study on I-80 in California”. Paper No. 22-01057, Washington, D.C., (2022).

Study Report: Download the Study Report Document

CMFs Associated With This Study

Category: Advanced technology and ITS

Countermeasure: Coordinated Ramp Metering

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
1.07-73 StarsAllAllPrincipal Arterial InterstateNot specified
0.9553 StarsAllK,A,B,CPrincipal Arterial InterstateNot specified
1.12-123 StarsAllOPrincipal Arterial InterstateNot specified
0.87133 StarsAllAllPrincipal Arterial InterstateNot specified
0.76243 StarsAllK,A,B,CPrincipal Arterial InterstateNot specified
0.9283 StarsAllOPrincipal Arterial InterstateNot specified
1.11-113 StarsAllAllPrincipal Arterial InterstateNot specified
0.9913 StarsAllK,A,B,CPrincipal Arterial InterstateNot specified
1.16-163 StarsAllOPrincipal Arterial InterstateNot specified