ALAMEDA AND SANTA CLARA COUNTIES — Caltrans District 4 (Bay Area) and its partners Metropolitan Transportation Commission (MTC), Santa Clara Valley Transportation Authority (VTA), Alameda County Transportation Commission (Alameda CTC) and cities along the Interstate 880 (I-880) corridor in Alameda and Santa Clara counties recently upgraded the existing ramp metering system to an adaptive ramp metering system.
Completion of the activation of all four phases of the job was achieved on September 9, 2022. The upgrade is expected to improve travel time reliability and lessen traffic congestion throughout the day. Weekend implementation is ongoing.
The metering lights along the I-880 corridor in Santa Clara and Alameda counties now go dark between 8 p.m. and 5 a.m., consistent with the I-880 corridor’s current express lane hours of operation. In addition, Caltrans has posted temporary advance warning signs of each impacted onramp to alert the traveling public of the changes in hours of operation.
Adaptive ramp metering, as it is called, is when the equipment controlling the metering lights senses congestion on the freeway and adjusts how long the lights stay red or green. This in turn controls the frequency at which vehicles enter the freeway and prevents large groups of vehicles, commonly referred to as platoons, from entering all at once.
Before the implementation, the project team performed public outreach to notify the traveling public of the changes in hours of operation. In addition to notifications on Caltrans’ and local jurisdictions’ websites, temporary advance warning signs were placed at the onramps one week before the implementation.
There are also permanent advance warning signs which were installed in compliance with the California Manual on Uniform Traffic Control Devices and Caltrans Ramp Metering Design Manual standards. The “METER ON” flashing beacons alert the traveling public when the ramp meters are operating.
Additional nonstandard signage requires Caltrans Headquarters’ review and approval for exceptions to the standards cited above, and may not be more effective than the placement of standard signs and flashing beacons. In addition, excessive roadside signage may be overwhelming and may cause the traveling public to ignore the message.
Also, since the ramp metering system is running on an adaptive algorithm, the metering light switches to solid green when the freeway can accommodate the traffic. A permanent advance warning sign with hours of operation might confuse the traveling public in such circumstances.
Additional signage on local jurisdictions upstream of entrance ramps is not recommended, as those signs may confuse the traveling public on local streets not intending to travel on the freeway, and because ramp metering signals and signs are limited to placement on the State highway rights-of-way.
Caltrans thanks motorists for their patience as we work to improve the Bay Area’s highways, bridges and tunnels.
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