SM 101 Express Lanes Project



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Toll Equipment Testing Now in Progress

Testing of tolling equipment is currently taking place on the new Express Lanes from the San Mateo County/Santa Clara County line to Whipple Avenue in Redwood City. This is in preparation for the Express Lanes opening soon. The Express Lanes are designed to move more people through the corridor while prioritizing carpools.

Travelers in this section of U.S. 101 may notice the change in lane striping and pavement markings in the existing high-occupancy vehicle (HOV) lanes. The existing lane stripe is being replaced with a skip stripe and the existing diamond shape is being replaced with the letters “EXPRS LANE”. See Exhibit 1 below for an example.

Pavement Markings

Exhibit 1: Express Lane pavement markings


“Under Construction” banners on the new overhead variable toll message signs are being replaced with “Toll Testing” banners. See Exhibit 2 below for an example.

Variable toll message sign during toll testing

Exhibit 2: Variable toll message sign during toll testing


During toll equipment testing, the lanes will continue to operate as HOV lanes, useable by vehicles with two or more people, Monday through Friday, between the hours of 5 AM – 9 AM and 3 PM – 7 PM. The lanes are open to all vehicles during all other times. There will be no charge for the use of the lanes UNTIL the Express Lanes are open, which will be signified by the removal of the “TOLL TESTING” banners from the new overhead variable toll message signs.

Follow the signs! Signage on the road is the best place to find out which vehicles can use the lanes and when. 

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.

Project Information


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. Express Lanes are expected to open from the San Mateo County/Santa Clara County line to Redwood City soon and from Redwood City to I-380 in late-2022. Existing carpool lanes are being converted to Express Lanes between the San Mateo/Santa Clara County line and Whipple Avenue (blue solid line) and new Express Lanes are being constructed between Whipple Avenue and I-380 (red stripped line).

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 is creating 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. See the Document Library for the latest Project Fact Sheet.

The Express Lanes are designed to maintain speeds of 45 miles per hour or greater, resulting in reduced and more reliable travel times. To learn more about how the Express Lanes will operate, see the image below and check out the Frequently Asked Questions and Project videos series.

What is an Express Lane?

  • Buses and 3+ carpools drive for free
  • Other drivers can choose to pay
  • Electronic toll collection
  • Dynamic tolls (congestion pricing) keep lane free flowing


How express lanes work


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 being completed 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 carpool lanes from the San Mateo County/Santa Clara County line to Whipple Ave in Redwood City were converted into Express Lanes.

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 are being constructed. Project construction is currently scheduled to last through mid-2022. Until then, construction activities occur on the freeway median, lanes, shoulders, ramps, and on local city streets. The freeway lanes are being repaved and restriped before each new lane segment is open for operations.

Construction activities 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.


Lane and Ramp Closures

Lane closures are implemented to facilitate work on the freeway lanes and ramps for the safety of crews and nearby travelers during construction activities. Freeway lane closures may occur on northbound and southbound U.S. 101 lanes from 9:00 PM to 5:30 AM, Sunday night to Saturday morning. Travelers can see real-time traffic conditions from changeable message signs placed in the construction zone. The Smart Traffic System was implemented during construction to provide up to date information, improve safety, and reduce congestion.

Ramp closures may occur on northbound and southbound U.S. 101 from Sunday night to Saturday morning from approximately 8:00 PM to 6:00 AM. Consecutive interchanges for northbound and southbound ramps will not be closed at the same time. Ramp closure information will be displayed on changeable message signs within the construction zone and detour signs will be posted.

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

Other Construction Activities

Sound Walls

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

Full Freeway Closures

As part of the Project, Caltrans is replacing 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.


 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)

ENVISION Silver Sustainability Award Factsheet (PDF)

ENVISION Hoja Informativa (PDF)