SM 101 Express Lanes Project


Upcoming Overnight Closures on U.S. 101

As part of the San Mateo 101 Express Lanes Project, Caltrans will be replacing a total of six overhead sign structures (that span the width of one side of the freeway, from the shoulder to the median) on U.S. 101. Due to the large size of these sign structures, it is necessary to close one direction of the freeway at a time. Caltrans has completed the removal of all six overhead sign structures and installed temporary orange roadside signs along the freeway shoulder on U.S. 101. 

Additional overnight freeway closures will be required to install new overhead sign structures in Fall 2021.

Click here to learn more about the closures.

Stay Informed and Plan for Delays

    Caltrans is constructing express lanes on U.S. 101 from the San Mateo County/Santa Clara County Line to I-380 in South San Francisco. Construction is expected to be completed in mid-2022 with the full lanes opening to traffic late-2022.

    To sign up for weekly or quarterly updates, email with the subject line 'Weekly' or 'Quarterly' to Follow @CaltransD4 on Twitter for Project updates. Para mayor información en español, visite de abajo. 更多详情的中文,请访问下面.

    101 Express Lanes Project Map January 2020

    Existing carpool lanes will be converted to express lanes between the San Mateo/Santa Clara County line and Whipple Avenue (blue solid line) and new express lanes will be constructed between Whipple Avenue and I-380 (red stripped line). This will result in 22 miles of express lanes in each direction of U.S. 101.

    Scroll down to read Project information, construction updates, Project contact information and link to documents. Also, click on the Frequently Asked Questions link above to read frequently asked questions and check out this week’s construction update by clicking the Construction Update link above. 

    Project Information

    Accessibility Assistance: Caltrans makes every attempt to ensure our documents are accessible. Due to variances between assistive technologies, there may be
    portions of these documents which are not accessible. Where documents cannot be made accessible, we are committed to providing alternative access to the content. Should you need additional assistance, please contact Alejandro Lopez at (510) 385-6856 or

    The San Mateo 101 Express Lanes Project is 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 will create 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 will seamlessly connect to the express lanes being constructed in Santa Clara County.

    A goal of the express lanes is to enable travel speeds of 45 mph or greater, resulting in reduced and more reliable travel times.

    How an Express Lane Operates

    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
    • Make upgrades to pavement and lane striping


    Construction of the San Mateo 101 Express Lanes is occurring in two phases:

    Phase One – San Mateo County/Santa Clara County Line to Whipple Ave: Phase One construction began in March 2019. During this phase, the Project is converting existing carpool lanes to express lanes from the San Mateo County/Santa Clara County Line to Whipple Ave in Redwood City. Minor construction activities will continue throughout 2020 and 2021.

    Phase Two – Whipple Ave to I-380: Phase Two construction began in February 2020. During Phase Two, the Project is constructing new express lanes from Whipple Ave to I-380 in South San Francisco. Project construction is currently scheduled to last through mid-2022. Throughout 2020, construction activities will occur on the freeway lanes, shoulders, ramps, and on local city streets. Beginning early 2021 through mid-2022, construction activities will occur in the freeway median. Lastly, the Project area will be repaved and restriped before the new lane is open for operations.

    Construction activities will require nightly freeway lane closures, temporary ramp closures, lane closures on city streets, and the relocation of some sound walls. See below for detailed information on anticipated Lane Closures, and Sound Wall Removal/Reconstruction.

    Lane Closures

    Due to current low traffic volumes, Caltrans has begun implementing nightly lane closures beginning at 7:00PM, and ending by 6:30AM, Sunday night to Friday morning. Caltrans will continue to provide real-time traffic conditions via changeable electronic message signs placed within the construction zone. Caltrans will monitor traffic delays and make adjustments as necessary, though project related delays are anticipated to be minimal during this time.

    Travelers will be able to see real-time traffic conditions from changeable message signs placed in the construction zone. The Smart Traffic System is being implemented during construction to provide up to date information, improve safety, and reduce congestion.

    Sign up for weekly updates to get details on the construction activities planned each week. 

    Sound Wall Removal/Relocation in San Mateo

    As part of project construction, Caltrans removed and relocated sections of sound wall in the City of San Mateo throughout 2020 and early 2021.

    Additional information can be found here.

    Para mayor información visite aquí.

    更多详情请访问 这里

    Project Contacts

    For questions during construction, or to request a presentation from a project representative, contact the Caltrans Public Information Officer:

    Alejandro Lopez at (510) 385-6856 or email

    To sign up for weekly or quarterly updates, email with the subject line 'Weekly' or 'Quarterly' to

    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 to learn about San Mateo 101 Express Lanes policy and governance!

    Documents Library

    February 2020 Project Announcement

    February 2020 Traffic Advisory

    January 2020 Project Announcement

    Project Fact Sheet (PDF)

    Hoja Informativa (PDF)

    情况说明书 (PDF)

    Vegetation Removal Fact Sheet (PDF)

    Hoja informativa sobre eliminación de vegetación (PDF)

    植被清除概况介绍表 (PDF)

    Vegetation Removal Map (PDF)