Caltrans Pushes 101 Expansion Through Equity Priority Communities

Transform is working with a coalition of local and regional advocates, including Rise South City and Sustainable South City, to stop a potential highway expansion project in San Mateo County. The project will likely add a new managed lane in each direction to a segment of Highway 101 stretching north from I-380 through Brisbane and South San Francisco to the San Francisco border. Caltrans has already expanded the highway on two segments directly south of the project area, which has failed to reduce congestion as promised. Fortunately, there’s a better solution: convert a general-purpose lane to a managed lane instead of expanding the highway.

The U.S. 101 project 

Caltrans began adding toll lanes to Highway 101 to manage traffic congestion and encourage carpooling in 2019. The first phase of the project, stretching from the San Mateo County/Santa Clara County line to Whipple Avenue, converted existing carpool lanes to express lanes that charged a toll and was completed in 2022. 

The second phase, from Whipple Avenue to the junction of I-380, involved building new lanes for the express lanes. Transform unsuccessfully opposed the widening option of the project, but we were able to secure an equity program that was the first of its kind in the U.S., with some of the toll revenues allocated to support low-income residents in San Mateo County. Nevertheless, the widening of 101 in southern San Mateo County will still lead to worse air pollution, congestion, and traffic violence in the lower-income neighborhoods adjacent to the highway.

Read our report about express lanes on Highway 101.

The next phase, from I-380 to the San Francisco City and County line, is scheduled to start construction in 2028. Caltrans will release an environmental impact report (EIR) in early 2026 to consider three alternatives: no build, convert existing lanes, and build new lanes. The project is sponsored by Caltrans, the San Mateo County Transportation Authority (SMCTA), and the City/County Association of Governments of San Mateo County (C/CAG). SMCTA gets its money from Measure A & W sales taxes approved by San Mateo County voters.  

An already environmentally burdened, equity priority community

CalEnviroScreen data shows that the neighborhood through which the next Highway 101 project will pass is already among the most burdened by pollution in California, with a heavy toll from diesel, particulate, and traffic pollution. In addition, South San Francisco is among the top 25% on the disadvantaged communities (DAC) index under SB 535. MTC has labeled this as an Equity Priority Community — i.e., a neighborhood with a large proportion of people of color, people with lower incomes, and people who are less likely to own automobiles.

These communities are often underresourced when it comes to fighting a huge, opaque bureaucracy like Caltrans. Transform is partnering with several community groups to lift up their voices and bring their concerns to the table in consideration of the various options for the managed lanes project. 

Caltrans has a history of ignoring or downplaying community concerns about the impacts of highway expansion on pollution-burdened frontline communities. A recent example of this is a freeway interchange project in Fresno that is going ahead despite community opposition.

Lane construction vs. conversion

Traffic congestion is a real problem that deserves real solutions. Managed lanes restrict access to high-occupancy vehicles or those paying a toll. 

However, building new highway lanes under the guise of creating space for managed lanes increases vehicle miles traveled, pollution, and greenhouse gas emissions. Plus, it is more expensive than converting existing lanes, so the revenue generated by the tolls is often directed toward repaying the cost of construction rather than supporting alternatives to driving, like transit and street safety. 

The existing lanes will still carry a heavy load of cars and trucks, and the new lane will encourage more people to take that route. Caltrans’ own guidance says that “a project that adds a new HOV lane could induce as many vehicle miles traveled (VMT) as a new general purpose lane would.” And a draft report from C/CAG shows traffic volumes on a section of 101 widened in an earlier phase of the project are close to or exceeding capacity. But unfortunately, this reality hasn’t stopped highway widening projects like this one from moving forward. 

There is no excuse for highway widening

Imagine if you had water running into your living room because of a leak in the roof. You could patch the living room ceiling, but the water would keep piling up behind the patch and, over time, you’d have to add to the patching to stop the drip. Or, you could simply fix the hole in the roof.

Adding highway lanes to solve traffic congestion is like patching the ceiling instead of the roof. Wider highways only temporarily decrease congestion, while they ultimately lead to more traffic through induced demand. 

Traffic congestion isn’t a freeway problem: it’s a housing and transit problem. People are forced into long commutes when there isn’t enough affordable housing near job centers. And even those who live closer are forced to drive when there is no convenient transit service.

The Highway 101 corridor is served by SamTrans, BART (as far south as Millbrae), and Caltrain. Widening the highway undercuts this rich transit capacity. Converting an existing lane to a managed lane and using the savings to boost bus and rail service would be a more sustainable and cost-effective solution. Money always seems to be available to widen highways; meanwhile, Bay Area transit operators struggle to secure enough funding to avoid a fiscal cliff.

Of course, Transform’s Moving San Mateo Forward report found that San Mateo County built only one home for every 19 jobs created between 2010 and 2015. Even higher-income workers have a hard time finding nearby housing because of a lack of housing density to match the density of employment. The California Housing Partnership found that a worker needed to earn at least $62.83 an hour to afford the average rent in San Mateo County without being rent-burdened. The long-term solution to congestion is increasing the supply of affordable housing and pairing it with better transit service.

Building highways while California burns

Transform’s Beyond Highways campaign seeks to move California beyond highway building as the only solution to our transportation problems. New highway lanes bake in decades more of climate-killing car and truck traffic. Caltrans cannot continue to build freeways as if climate change doesn’t exist. Thankfully, Caltrans is not the only decision maker. The SMCTA and C/CAG are also sponsors of the project and have the opportunity to champion a lane conversion instead of more highway expansion. 

Transform and our partners will be engaging the community and meeting with San Mateo elected officials in the coming months. When Caltrans releases the environmental impact report in early 2026, we’ll be ready to mobilize strong feedback in response to any alternatives that widen the highway. 

In the meantime, please sign our petition to stop the widening. That’s the best way to stay in the loop about upcoming actions and opportunities for this work.