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(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
| 1.07 | -7 |  | All | All | Principal Arterial Interstate | Not specified |
| 0.95 | 5 | | All | K,A,B,C | Principal Arterial Interstate | Not specified |
| 1.12 | -12 | | All | O | Principal Arterial Interstate | Not specified |
| 0.87 | 13 | | All | All | Principal Arterial Interstate | Not specified |
| 0.76 | 24 | | All | K,A,B,C | Principal Arterial Interstate | Not specified |
| 0.92 | 8 | | All | O | Principal Arterial Interstate | Not specified |
| 1.11 | -11 | | All | All | Principal Arterial Interstate | Not specified |
| 0.99 | 1 | | All | K,A,B,C | Principal Arterial Interstate | Not specified |
| 1.16 | -16 | | All | O | Principal Arterial Interstate | Not specified |
