Starting April 8, 2025 In Sunnyvale, Mountain View, Palo Alto, and Redwood City
SAN MATEO and SAN CLARA COUNTIES — Caltrans District 4 (Bay Area) is working with the Metropolitan Transportation Commission (MTC), the Valley Transportation Authority (VTA), the City/County Association of Governments, and various cities to activate an Adaptive Ramp Metering (ARM) system along the U.S. 101. The ARM system aims to reduce traffic congestion on the mainline freeway from 5 a.m. to 8 p.m. daily.
The new system will be located between Sunnyvale in Santa Clara County and Brisbane in San Mateo County. Currently, the metering lights on this corridor operate based on preset hours during weekday peak periods and local traffic flow and do not account for downstream conditions. The new ARM system will dynamically adjust metering rates based on the downstream conditions.
Timeline: Upgrades will be performed in four phases. Beginning on April 8, upgrades will be installed between Sunnyvale and Redwood City. The second phase is planned for May 2025 in the northern end of U.S. 101 in San Mateo County between the Harney Way interchange in Brisbane and the Whipple Avenue interchange in Redwood City. The third is planned for June 2025 from the Lawrence Expressway interchange in Sunnyvale to Bernal Road interchange in San Jose. The last phase is forecasted for July 2025 from the Bailey Avenue interchange in Morgan Hill to the Monterey Road interchange in Gilroy. Activation for the weekends within the scope of those four phases will begin in September 2025. Caltrans estimates the project will be complete by October 2025, including rollout and monitoring.
Caltrans will post signs at each impacted on-ramp to alert the public of the change in hours of operations. The ramp meter signals will go dark between 8 p.m. and 5 a.m., consistent with the current Express Lane operating hours in the corridor.
Ramp metering is a proven congestion management tool that makes merging easier, reduces the potential for collisions, reduces freeway congestion by smoothing out traffic flows, delivers more consistent and reliable travel times and improves air quality.
Caltrans is committed to using ramp metering as an effective traffic management strategy to maintain an efficient freeway system, and providing a safe and reliable transportation network that serves all people and respects the environment.
For 24/7 traffic updates, follow 511.org: https://twitter.com/511SFBAY. For real-time traffic, click on Caltrans QuickMap: http://quickmap.dot.ca.gov/.
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