Is Coordinated Ramp Metering (CRM) Improving California Traffic Safety and Congestion?

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MTI research reveals CRM implementations in two major California roadways show improved system efficiency
May 5, 2020
San José, CA

Coordinated ramp metering (CRM) is a critical component of creating smart freeway corridors, which manage traffic congestion and improve safety. New Mineta Transportation Institute research, Evaluation of Coordinated Ramp Metering (CRM) Implemented by Caltrans, examined the recent CRM implementations on Interstate 80 (I-80) in the Bay Area and State Route 99 (SR-99) in Sacramento. To identify significant efficiency improvements, researchers looked specifically at travel time reliability measures and before-an-after evaluations using the Empirical Bayes (EB) approach.

With the goal of improving efficiency and safety, CRM uses an algorithm that considers real-time traffic volumes on freeway mainlines and ramps and then adjusts the metering rates on the ramps for optimal flow along the entire corridor. This study used the ratio of vehicle-miles traveled (VMT) and vehicle-hours traveled (VHT) for the corridor segments as measures of system efficiency.

To measure the before-and-after effect of the CRM systems, researchers went beyond the typical data comparison of the corridor before and after implementation, which was found to have too many confounding variables aside from CRM implementation. Instead, explained principal investigator, Dr. Anurag Pande, “We established the counterfactual or what would have happened on the study corridors without CRM, by using control corridors from the same Caltrans district.”

Findings revealed that CRM systems in Caltrans Districts 3 and 4 have seen significant improvements in terms of system efficiency. The results show that the I-80 Eastbound corridor showed an increase in efficiency as high as 6.3% (during November 2018) compared to the counterfactual scenario, with 17 out of the 24 months in the “after” period showing improvements.

However, travel time reliability continues to be inconsistent. Estimation of safety improvements requires additional crash data, which will be collected over the next two years and compared with the counterfactual estimates provided in the report.


At the Mineta Transportation Institute (MTI) at San Jose State University (SJSU) our mission is to increase mobility for all by improving the safety, efficiency, accessibility, and convenience of our nation's transportation system. Through research, education, workforce development and technology transfer, we help create a connected world. MTI was founded in 1991 and is funded through the US Departments of Transportation and Homeland Security, the California Department of Transportation, and public and private grants. MTI is affiliated with SJSU’s Lucas College and Graduate School of Business.


Dr. Anurag Pande is a Professor of Civil Engineering at California Polytechnic State University, San Luis Obispo (Cal Poly). Dr. Amir Molan and Dr. Alireza Shams are lecturers in Civil Engineering at Cal Poly. Dr. Cristina Tortora is an Assistant Professor in the Department of Mathematics and Statistics at San Jose State University (SJSU). Nivedha Murgesan is working towards her Master of Science in Statistics at SJSU. Faridur Rahman is a transportation engineer at GDM Engineering Solution. Jacky Loh is a traffic designer at RailPros.



Irma Garcia, MTI Communications & Workforce Development Coordinator



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