San Mateo County Highway 101 – Managed Lanes Project (MLP)

South San Francisco, CA   January 14, 2019 Submitted by Department of Transportation

Getting More Passengers through the Busy Corridor

Silicon Valley produces between 20- 25% of California’s annual gross domestic product. This economic juggernaut has fueled revenue and job growth, but it has also created overcrowding on San Mateo Highway 101, the major commute route between San Francisco and Silicon Valley.

Year after year, the rush hour starts earlier in the morning and ends later in the evening. Travel times have increased while predictability has decreased. A stalled vehicle at peak hour can create a ripple effect lasting for minutes or hours, depending on how quickly a tow truck can weave through backed-up traffic. The impacts are economic as well as social. More time commuting means less productive time at work and fewer hours for relaxing at home.

Getting people out of their cars and onto transit has helped, but it’s difficult to promote bus riding when a significant incentive is lacking: Highway 101 in San Mateo County has no carpool lanes north of Whipple Avenue, forcing buses and carpoolers to travel in the same congested lanes as solo drivers.



A Solution for an Urban Corridor

Long-time Peninsula commuters know that Caltrans has widened Highway 101 many times. Which begs the question: Is there any space left over for a widening project.?

Suprisingly, the answer is yes. Caltrans engineers discovered that by shifting the centerline of the freeway, threading it through the right of way, they could build within the existing limits. This means that much of the freeway needs to be reconfigured during construction, but the time and money saved by eliminating right of way acquistions will be enormous. Construction on this $514 million project will begin in the winter of 2019 with an estimated completion of Fall 2021. Project funding comes from a variety of sources including SB 1 funds.


Planning the Project Caltrans will convert the existing northbound and southbound auxiliary lanes into through-lanes, and change the far left lanes into express lanes.

At Whipple Avenue, the new express lanes will connect with existing carpool lanes. Caltrans will convert these carpool lane into express lanes. The joining of express lanes will create two 22-mile long express lanes.

How will this be done?

  • Connect all auxiliary lanes in San Mateo County, converting them into through-lanes.
  • Construct new auxiliary lanes where they are needed.
  • Convert the HOV lanes from Whipple Avenue to Matadero Creek into Express Lanes
  • Build a tolling system that uses FasTrak to collect tolls

Why an Express Lane

Caltrans studied many options before concluding that express lanes would be the most effective means of lessening congestion in the corridor.

When traffic engineers looked at building a typical lane, a lane with no restrictions on occupancy, they found – not surprisingly – that the new lane would be overused and congested the very day it opened. On the other hand, when they studied building a carpool lane, they found it would be underutilized, even during carpool hours.

Between these two choices, is the express lane option, which allows buses and carpools to travel free of charge while selling the excess capacity to drivers willing to pay a toll. When the toll-paying vehiciles move into the express lane, they will lower congestion in the mixed flow lanes.

Managing the Express Lane

The traffic manager will monitor the express lane and raise and lower the toll as necessary.

Picture the traffic manager using a large dial to keep the lane runing smoothly. When the manager sees that the express lane is slowing down as a result of too much traffic, the traffic manager turns the dial to the right, increasing the toll on non-carpoolers and reducing demand for the lane.

If the traffic manager sees large gaps between vehicles in the express lane, the manager turns the dial to the left, reducing the toll and increasing demand for the express lane. As noncarpooler enter the express lanes, they reduce congestion in the mixed flow lane.

Carpoolers with 3 or more persons will always be exempt from tolls. All other things being equal, (traveling at the same time, through the same location) a vehicle with two passengers will pay a smaller toll than a single occupant vehicle. Traffic engineers have guidelines for predicting congestion based on traffic volumes. Caltrans looks for a traffic volume of between 1600-1650 vehicles per hour to keep congestion from occurring in the express lane.

Proposed hours of operations are 5:00 AM – 8 PM.

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Related Reading:

Silicon Valley Express Lanes:

San Francisco Transportation Authority Study of Carpool and Express Lanes:

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