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Open Access Publications from the University of California

California PATH is a unique research organization. It focuses on solving California's and the nation's transportation problems by conducting relevant and high-quality research that advances the state of the art. The research is performed by a statewide group of faculty, graduate students, and research staff of diverse backgrounds and expertise working closely together. At the same time, PATH produces the next generation of leaders in academia and the transportation profession. PATH's ongoing research directly addresses the mobility, reliability, and safety goals of our Caltrans (California Department of Transportation) partners and will place major emphasis on field testing of the most promising strategies for traffic control, traveler information, intersection safety, transit, and other mobility options.

Alexander Skabardonis, Adjunct Professor of Civil and Environmental Engineering and Research Engineer at the Institute of Transportation Studies, is PATH's director.

Cover page of Early Opportunities to Apply Automation in California Managed Lanes

Early Opportunities to Apply Automation in California Managed Lanes


Connected and automated vehicles hold the potential for substantial improvements to traffic safety, travel time reliability, roadway capacity, and environmental impacts and managed lanes have the potential to be ideal testbeds for CAV technologies. The purpose of this report is to identify specific opportunities to leverage California’s managed lane network as early experimental and pilot deployment sites for CAVs. To this end, we have conducted a detailed inventory of the managed lane facilities in California and applied evaluation criteria to identify two promising sites for future CAV tests and initial deployments. Our study recommends the I-15 Express Lanes in San Diego and the I-10 Express Lanes in Los Angeles for future CAV tests.


In this report, we have also documented the major CAV applications that are being considered by USDOT for near-term deployment. After assessing which of the CAV applications are best suited for deployment in managed lanes, we selected the following five applications to be considered for testing in the two California sites: highway CACC, V2I speed harmonization, freeway merge coordination, automated bus rapid transit, and automated barrier mover vehicle.


Next, we presented conceptual test and deployment plans for those five CAV applications along with various testing scenarios. We then presented an analysis of the likely timeline for testing and pilot deployment and related vehicle and infrastructure requirements of those applications. For most of the applications, there will be at least two years of preparation required before testing or initial deployment can occur. Finally, our report describes the expected benefits of deploying the selected CAV applications at the proposed sites including increased capacity, reduced congestion and smoother traffic flow in managed lanes and some related improvements to safety.

Cover page of Field Experiment of Variable Speed Advisory (VSA) Final Report

Field Experiment of Variable Speed Advisory (VSA) Final Report


This report documents the field test of Variable Speed Advisory (VSA) which is an Active Traffic Management strategy.  The test site for the VSA is on State Route 78 Eastbound (SR-78E) from Vista Village Drive (in the City of Vista) to the freeway interchange point of SR-78E and U.S. Route 15 (in the city of Escondido).  This test segment is a three-lane freeway with a posted speed limit of 65 mph and it has 10 on-ramps and 10 off-ramps.  The project was funded by the California Department of Transportation (Caltrans) Division of Research Innovation and System Information (DRISI) under Contract Number 65A0587.  Real-time traffic detector data including flow, speed, and occupancy from pre-existing loop detectors in the field test site, were transmitted via the internet by engineers at Caltrans District 11 (D11) Transportation Management Center (TMC) to a server located in the offices of California Partners for Advanced Transportation Technology (PATH).  This data was then aggregated with real time speed data, captured every 30s [seconds] by radar equipment installed along with solar panel powered LED display equipment, for the display of a VSA, at 7 different sites along a 10.8 mile section of SR 78E.  These two sources of data were then processed for the estimation of the overall traffic state along the corridor, which was in-turn used to calculate the VSA for each section in order to maximize overall traffic throughput through recurrent bottlenecks on SR-78E.  Calculated VSA values were then rounded to multiples of 5 mph and displayed on the VSA signs.  Public outreach was conducted by Caltrans D11 Public Information Office (PIO) to educate the public about the VSA test, and encourage their compliance with posted speed advisories.  A publicly accessible website was also developed for the real-time display of Google Traffic, traffic state, and VSAs displayed in the field.  This site was used extensively by Caltrans management, the project team, and by the public drivers.  After different stages of the system development, integration, and installation process were completed, a progressive test procedure was executed to mitigate any potential negative impacts on traffic operation.  This procedure included dry-runs (saving data for analysis without roadside display), error detection, system tuning, preliminary testing, and extensive tests for data collection for four weeks.  The results of the performance analysis, conducted with an independent PeMS data set, illustrated an improvement in three performance measures for the AM (6-9AM) peak hours: Vehicle Miles Traveled (VMT) increased by 2.72%; Vehicle Hours Traveled (VHT) decreased by 6.28%, and the average speed over the road segment or Q=VMT/VHT increased by 8.71%.  In PM peak hours (2-7PM), two of the three performance measures improved: VMT did not have noticeable improvement; VHT decreased by 1.47% on average;  and Q increased by 2.80% on average.

Cover page of Congestion-Responsive On-Ramp Metering: Recommendations toward a Statewide Policy

Congestion-Responsive On-Ramp Metering: Recommendations toward a Statewide Policy


The objective of this project was to develop recommendations toward a statewide policy of congestion responsive freeway ramp metering (CRRM) operation. The research has been performed in the following approaches: First an empirical “before” and “after” freeway corridor performance evaluation was performed on a selected set of California’s freeway corridors that had implemented congestion responsive ramp metering. Next, other important policy and operational factors that impact the effectiveness of extended hours ramp metering were evaluated: traffic detector health and data quality and their potential impact on CRRM operation, immediate operation hours, ramp metering (RM) light setting to “Green-Ball” or “Black”, on-ramp storage capacity effects and some alternative solutions to reduce/avoid queue-override, and properly handling institutional relevant issues to gain support from local jurisdictions. The corresponding recommendations are included in this report.