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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 Improved Analysis Methodologies and Strategies for Complete Street

Improved Analysis Methodologies and Strategies for Complete Street


Complete streets movement is a national effort to return to traditional streets in our cities to enhance livability, safely, accommodate all modes of travel, provide travel choices, ease traffic congestion, and promote healthier communities. The California Department of Transportation (Caltrans) and several local agencies in the State have developed implementation plans for complete streets. In this project, we developed and tested improved strategies and analysis methodologies for complete streets, taking into consideration the emerging advances in technology on control devices and data availability from multiple sources. The proposed improvements to the Highway Capacity Manual (HCM) methodology for bicycle LOS, accounts for protected bicycle lanes, traffic exposure, bicycle delay and pavement quality index. A survey was also used to calibrate the proposed bikeway evaluation models. Signal control strategies for complete streets were developed and tested, including signal optimization for pedestrians, bicycles and Transit Signal Priority (TSP) along major travel corridors in San Francisco.

Cover page of Potential Erroneous Degradation of High Occupancy Vehicle (HOV) Facilities

Potential Erroneous Degradation of High Occupancy Vehicle (HOV) Facilities


This document is the final report for Task ID 3710 (65A0759), a project titled “Potential Erroneous Degradation of High Occupancy Vehicle (HOV) Facilities”. This report contains a compilation of three previous technical memorandums titled “Survey of Data-Mining Methods”, “Performance of Methods”, and “Magnitude of HOV Degradation”. HOV lane sensors in Caltrans’ Performance Management System (PeMS), are sometimes misconfigured as general-purpose lanes. In this situation, HOV lane data is mistakenly aggregated with general-purpose lane data and vice versa. The purpose of this project was to understand how widespread this problem might be and the extent to which it impacts performance reporting on the degradation of HOV lanes.

Cover page of Evaluation of Coordinated Ramp Metering (CRM) Systems in California

Evaluation of Coordinated Ramp Metering (CRM) Systems in California


Freeway on-ramp metering (RM) has been extensively used as a traffic control strategy to regulate the entry of the on-ramp vehicles to prevent congestion at the freeway merging areas and preserve the freeway capacity. Benefits of RM include improved freeway travel times, improved travel time reliability, and accident reductions. Fixed-rate ramp metering strategies are based on historical data and implemented by time of day. Traffic responsive RM strategies are based on real time freeway traffic data provided by loop detectors at the vicinity of the on-ramp. Coordinated RM determine the metering rates at the ramps along a freeway corridor to minimize the delays or maximize the freeway throughput. The objective of this research was to evaluate the traffic performance of coordinated traffic responsive systems (CRM) currently implemented by Caltrans based on field data.

Cover page of Hybrid Data Implementation: Final Report for Task Number 3643

Hybrid Data Implementation: Final Report for Task Number 3643


This report investigates how Caltrans may incorporate third-party vendor data into its established system for performance measurement to improve accuracy of vehicle hours of delay (VHD) estimates and to enable smarter deployment of point-based sensors, such as loops. Methods are evaluated to project data from multiple sources, including multiple vendors and internal data feeds, onto the same domain of analysis so as to compute performance metrics with high fidelity. The recommended VHD estimation method depends on the infrastructure type and the data available. Overall a hybrid approach provides the best estimates of performance measures. A roadmap is proposed to begin using hybrid traffic data and to create opportunities to modify existing usage strategies of point-based sensors.

Cover page of Improving the Traffic Census and Highway Performance Monitoring System (HPMS) Programs

Improving the Traffic Census and Highway Performance Monitoring System (HPMS) Programs


The objective of this research study was to support the Traffic Census and Highway Performance Monitoring System (HPMS) Programs in identifying locations for motorized traffic data collection on public roads in California.  


The study analyzed the traffic census count locations for each District to determine at which Census count locations the automated and continuously collected Caltrans Performance Measurement System (PeMS) data could be used in lieu of manual traffic counts. 


Next, this research identified and evaluated count locations for motorized traffic data collection on non-State Highway System Routes to help meet Federal Highway Administration (FHWA) requirements for the Caltrans Highway Performance Monitoring System (HPMS) program.


Lastly, this research reviewed and summarized the emerging traffic data collection technologies and data sources appropriate for Caltrans HPMS and/or Census reporting purposes. 


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.