Improving Freeway Operations Using Real-Time Adaptive Ramp Meters - A Case Study for I-680 Southbound Corridor in Alameda County, California

Ramp metering has the potential to improve the operation of congested freeway facilities. Real-time adaptive freeway ramp meters have been increasingly popular among public agencies in the United States to manage freeway traffic operations. The basic principles to improve operations are by managing demand at freeway entry ramps and reducing freeway merging problems created by the arrival of platoons of traffic. This paper provides an overview of a ramp metering plan development process, including assembly of the project development team, coordination amongst stakeholders, performance of technical studies, and development of a timeline for implementation for the Interstate I-680 southbound corridor in Alameda County, California. The paper focuses on the technical evaluation required to develop metering rates in response to variable real-time freeway mainline conditions. It describes methods employed and challenges encountered in collecting data, identifying and bottlenecks and their causes, developing models to optimize meter rates without adversely affecting local streets, developing a metering rate plan that could respond to changes in freeway occupancy within a time of day context, field implementation and fine-tuning, and documenting the effectiveness of the program.