SM 101 Express Lanes Project

Caltrans, the San Mateo County Transportation Authority, the City/County Association of Governments, and the San Mateo County Express Lanes Joint Powers Authority have constructed Express Lanes on U.S. 101 from the San Mateo/Santa Clara County line to I-380. The project was completed in March 2023. To learn more about using Express Lanes in San Mateo County, visit 101expresslanes.org.

Map shows that the segment from the San Mateo/Santa Clara County line to Whipple Avenue opened in February 2022 and the segment from Whipple Avenue to I-380 opened in March 2023.

Project Information

The San Mateo 101 Express Lanes Project was a multi-year, multi-agency project initiated to reduce traffic congestion and encourage carpooling and transit use on U.S. 101 in San Mateo County. The Project created 22 miles of Express Lanes in both directions on U.S. 101 from the San Mateo County/Santa Clara County line to I-380 in South San Francisco. The San Mateo 101 Express Lanes seamlessly connect to the Express Lanes in Santa Clara County.

The Express Lanes were designed to maintain speeds of 45 miles per hour or greater, resulting in reduced and more reliable travel times. For more information about how to use the Express Lanes, visit 101expresslanes.org.

To learn more about how the SM 101 Express Lanes project and its construction, see the image below, check out the Frequently Asked Questions, and see the Project video series.

What is an Express Lane?

Buses, 3+ carpools (vehicles with three or more occupants), and motorcycles drive for free
Other drivers can choose to pay
Electronic toll collection
Dynamic tolls (congestion pricing) help keep lane free flowing

Key Project Benefits

Reduce congestion in the corridor
Increase person throughput (the number of people moved)
Encourage carpooling and transit use
Improve travel time and reliability for Express Lane users
Use modern technology to manage traffic
Upgrade pavement and lane striping

Project Construction

Construction of the San Mateo 101 Express Lanes was completed in two phases:

Phase One – San Mateo County/Santa Clara County line to Whipple Ave: Phase One construction began in February 2019. During this phase, the carpool lanes from the San Mateo County/Santa Clara County line to Whipple Ave in Redwood City were converted into Express Lanes. The lanes opened for tolling in March 2022.

Phase Two – Whipple Ave to I-380: Phase Two construction began in February 2020. During Phase Two, new Express Lanes from Whipple Ave to I-380 in South San Francisco were constructed by connecting auxiliary lanes to create an extra through lane of traffic on both northbound and southbound U.S. 101. The lanes opened for tolling in March 2023.

Project Contacts

To ask a question about construction, contact the Caltrans Public Information Officer:

Alejandro Lopez at (510) 385-6856 or email 101express@dot.ca.gov.

The management and operation of the San Mateo 101 Express Lanes is governed by the San Mateo County Express Lanes Joint Powers Authority (SMCEL-JPA), a six-member joint powers authority consisting of three San Mateo County Transportation Authority (SMCTA) Board members and three City/County Association of Governments of San Mateo County (C/CAG) Board members. Visit 101ExpressLanes.org to learn about San Mateo 101 Express Lanes policy and governance.