On a waterlogged highway, cars drive into the sea. Truck cabs and bus windows poke up above the waves; sedans are fully submerged, burbling through the water like schooling fish.
This is not a scene from a disaster movie, or an apocalyptic dream: it’s a virtual tour of what State Route 37 may look like in 2100, created by the California Department of Transportation to help us all wrap our heads around the stakes of this highway’s imminent plight. SR 37, which runs as two lanes between Novato and Vallejo on the northern shore of San Pablo Bay, is already getting soggy. Set right on the lip between the Bay and tens of thousands of acres of former wetlands, the highway is subject to flooding and hours-long traffic backups, and kept dry by pumps.
Now one piece of the fix is ready to break ground after years of planning. A $73 million grant from the California Transportation Commission has closed the funding gap for the next phase of the project: widening the eastbound lanes and lifting a flood-prone stretch known as Strip Marsh East. It’s a sliver of a sprawling puzzle that’s only beginning to take shape.
How do you solve a problem like State Route 37? The goal is to design a new highway that works for commuters and allows the San Pablo Baylands to be restored to the tides. But dig into how a new highway might look, and many more variables emerge: the wetlands, yes, but also equity issues, vehicle emissions, endangered species, bus access, biker access, hiker access, sediment supply, and wildfire escape routes, to name just a few. It’s a giant Rubik’s cube of concerns: snap a few interests into place, and others get thrown off. Plus there’s the issue of fully funding the project in an era where California is not primed to be particularly competitive in the federal arena. Dozens of agencies are spending thousands of hours trying to untangle the knot. “Threading this needle is really tough,” said James Muller, a program manager at the San Francisco Estuary Partnership, a governmental organization working on Baylands strategy that intersects with the highway’s planning. “As public servants, we need to sit in the middle of all of those needs, and in that tension.”
Yet the big-picture challenge is simple. In 15 to 25 years, large portions of SR 37 will be underwater. By 2100, the highway will become an Atlantis-esque waterscape. Before then, something has to change.
The SR 37 vision board
Planning a highway at the edge of a rising bay has required an almost science fiction-esque brainstorm, like setting up a colony on Mars: hostile conditions, limited resources, and a long list of life-support systems that have to work in tandem. In 2022, Caltrans released some possible solutions. The agency’s Planning and Environmental Linkages study took two years and accounted for such varied concerns as salt marsh harvest mouse habitat, earthquake fault zones, and the location of mineral deposits for “potential future exploitation.” “There’s lots of opportunities here,” said Jeremy Lowe, a senior environmental scientist at the San Francisco Estuary Institute. “There’s lots of pitfalls as well. I mean, if you build it wrong, then you just make problems worse.”
The conclusions came together after an unprecedented amount of conversation, in particular, between transportation agencies and environmental agencies. Caltrans and the Metropolitan Transportation Commission (MTC) are leading the project, but they’re coordinating with a group dubbed the Resilient 37 Collaborative, which includes a dauntingly long list of partners, including environmental agencies, tribes, elected officials, and nongovernmental groups like SFEI. Jeanette Weisman, MTC’s SR 37 Corridor program manager, describes this dialogue as “rocky,” but also “worth it.” The organizations speak different languages, use different acronyms, and have their eyes on different sets of concerns. “It’s improved some of our decisions, even if it was difficult and painful. Sometimes, it’s some of that hard love.”
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One possible solution was temptingly simple: scrap SR 37 altogether and route drivers up and over on State Route 12, instead. That would get the highway off the wetland entirely. It was also, though, an inequitable option, because the better-paying jobs are mostly in Sonoma and Marin, while Solano is where many workers can actually afford to live. Scrapping it would push people’s commutes into punishing territory. The wetland-friendliest route would deal a harsh blow to the people with the fewest resources.
Ultimately, the PEL narrowed the options down to “Alternative 5”: a causeway, raised off the water, that will essentially follow the path of the existing highway. The tentative design has four lanes, shoulders, and bicycle and pedestrian access, adding a segment to the Bay Trail. Ecologically, Alternative 5 is far from perfect—it’s still a road through a wetland—but it’s a lot better than what we have now. If the new highway is raised so that water can flow underneath—and the old highway removed—the San Pablo Baylands could be reconnected with the tides, potentially opening nearly 50,000 acres of wetlands for restoration. That’s bigger than the combined area of San Francisco and Berkeley.
“The opportunity to, hand in hand, make a transportation corridor resilient to sea level rise, and at the same time enable and deliver an ecological restoration on the order of the North Bay Baylands—to me, that is fairly, if not completely unique,” says Weisman. “I feel like we have an opportunity to make that [South Bay] Salt Pond restoration small potatoes.”
How to fix a sinking highway? Bridge by bridge.
The long-term vision is decades and a big pile of money away. Construction is expected to cost $6–11 billion, and gone are the halcyon Biden-era days of free-flowing federal dollars for climate-friendly transportation. Therefore Caltrans is proposing to bite off successive chunklets of highway project over several decades to reduce flooding and relieve congestion, starting with two lengthened bridges over Tolay and Novato creeks, and a lane-widening project between Sears Point and Mare Island. The problem is, even the chunklets are expensive. For example, building just one small component of the highway to the long-term height—the Tolay Creek Bridge, which is about halfway across San Pablo Bay—is expected to cost $750 million.
In a no good, very bad funding situation, that might as well be $750 billion. California Department of Fish and Wildlife Director Charlton H. Bonham acknowledged this in a December 2024 letter to the directors of MTC and Caltrans: “[I]t is obvious that neither MTC nor Caltrans has a path to secure the estimated $750M needed for the long-term project. Moreover, the fate of the Bipartisan Infrastructure Law and Inflation Reduction Act is now uncertain,” he wrote. “Given this reality, MTC and Caltrans maintain that the long-term project is impractical at this time.” It’s disappointing, he continued—but in the meantime we still have to do something. Hence the interim projects.
For many advocates of the long-term vision, these projects are hard to swallow. Why throw more sediment and asphalt and dollars into highway sections that will be swimming with the fishes in a mere 25 years—or even sooner? Environmental agencies and NGOs are eager to get down to building the permanent causeway. On the other hand, the updates are billed as preventing two decades of gridlock and flood closures for the residents of Solano County. It’s a clash of priorities on different time scales. So as long as the temporary mini-projects are moving forward, the eco-focused groups are trying to at least squeeze as many ecosystem benefits out of them as possible.
Many of the Resilient 37 partners I spoke to seem to see the interim projects as a test of the transport agencies’ willingness and ability to work together with environmental agencies. “Some people are saying, ‘Well, you’re sacrificing the long term for the near term,’ and it’s exactly the opposite,” said Larry Goldzband, executive director of the Bay Conservation and Development Commission (BCDC), a state agency charged with protecting the Bay. “You have to have the near term in order to demonstrate that you’re able to do this kind of work.”
So what will these three interim projects actually look like? Each is a test of whether transportation and ecological goals can actually coexist on a skinny stretch of sinking highway. Together, they’re a mix of compromise, experimentation, and progress.
Project #1: A not-very-permanent bridge
Tolay Creek is a small, scrubby stream at the juncture of SR’s 37 and 121, traversed by a two-lane, aging bridge. This tiny aperture is the only connection between the Bay and thousands of acres of salt marsh east of the highway. “You’ve got this potentially huge Slurpee upstream of Highway 37,” said Christina Toms, an engineer with an eye for metaphor at the San Francisco Bay Regional Water Quality Control Board. “And you’ve got a tiny, tiny straw at the Highway 37 bridge at Tolay Creek that connects much of those areas to San Pablo Bay.” Unless that bottleneck is widened, potential wetland restoration in the area is limited—Tolay Creek simply can’t handle the amount of water that would need to flow in and out of the marsh.
The new bridge at Tolay Creek will be longer, allowing the creek to widen, enabling more wetland restoration. That’s great news, because the clock is ticking—the wetlands need to be restored to health soon if they’re going to have a shot at surviving sea-level rise.
The bad news is that the bridge isn’t being substantially raised. So it’ll all have to be replaced when waters rise beyond an additional foot or two.
Project #2: A bridge that won’t have to be replaced
Over at the new Novato Creek bridge project, near the western tip of SR 37, it’s looking a little better for the long-term vision: not only will the new bridge increase watershed connectivity, it’s being planned at an elevation of 26 feet. The new bridge will be able to accommodate 7.1 feet of sea level rise by 2130, the “intermediate-high risk” projection from the California Ocean Protection Council. That means it’s at least one piece that likely won’t have to be replaced; instead, it can be patched straight into the new causeway as it goes up, chunk by chunk. This project is in line for $155 million of BIL money—which could be shaky under the Trump administration. However, so far, so funded.
“It’s really the first time I’ve seen where transportation planning and restoration planning are being integrated with each other, and not just doing it separately and then looking at each other’s plans as constraints,” says Xavier Fernandez, a division manager at the Water Quality Control Board. “It’s very exciting.”
Project #3: A marsh-friendly road-widening
The initiative to add HOV lanes in the stretch of road between Sears Point and Mare Island comes with an ecological silver lining: a plan to restore a long belt of high marsh called Strip Marsh East, which protects SR 37 from erosion and flooding. If the highway is raised, this strip will also protect marshes to the north. It’s a great candidate for restoration because it’s in better shape than a lot of the diked and subsided high marsh in the Bay. But it’s still full of water that doesn’t drain, which has caused the loss of high marsh vegetation that endangered species, like the salt marsh harvest mouse, rely on. Without its pickleweed to hold it together, Strip Marsh East is slowly deteriorating.
“Fixing the drainage problem here has been a goal of a lot of folks in the tidal wetland conservation and restoration community because we have so little high marsh habitat,” Toms tells me. “You want to stop the bleeding before you try to save the patient. And so that’s what this Strip Marsh East project is going to do.”
The critics’ case
Not everyone’s on board with these interim projects. Critics like nonprofit coalition ClimatePlan have labeled them half-billion-dollar “boondoggles,” dangerous distractions that expand driving while the Bay keeps rising. Jeanie Ward-Waller, a clean transportation lobbyist and project director for ClimatePlan, says Caltrans should ditch the temporary projects and put its time and dollars towards making the Alternative 5 causeway happen ASAP. ClimatePlan, which includes groups like 350 Bay Area and the Sierra Club, has lobbied state legislators against the $73 million lane expansion grant, and Ward-Waller testified this year against a state bill aiding the interim projects’ implementation (it passed anyway).
She’s not convinced the interim improvements will even last us until 2050, given that we have so far failed to curb global emissions. And driving, famously, doesn’t help. “Part of the case we’ve been making is: widening this corridor, increasing driving, is only contributing to the problem,” she says. “It just seems totally counterintuitive.” The highway planners and their critics agree on the destination—easier commutes, restored wetlands, a highway that doesn’t flood—but not on the path being taken to get there.
Still, Ward-Waller’s not dismissing everything outright. The transport agencies are planning to add public transportation options, for example, and “that is an equity solution,” she says. “But that could be done by just tolling the existing lane and not paying for this extremely expensive widening project that requires years of construction and, frankly, misery.”
So far, these alternative ideas have gotten little traction. MTC’s Weisman acknowledges the concern that adding lanes will increase driving, but she believes that the toll on the added lane and new public transport will discourage solo driving and offset the corridor-widening’s effect. As for Ward-Waller’s idea of just tolling the existing lane, she says, “there’s not a process for doing that scenario where we just add in a toll facility.” The current norm for such projects is that the only way to justify a toll to the driving public is to provide a new service.
Ward-Waller, who was once a Caltrans executive, feels that such norms are causing the transport agencies to fail to consider the “better ways to get there that would be more cost-effective and have a bigger equity benefit.” (She was demoted in 2023 after she raised questions about two construction projects that were allegedly circumventing environmental rules, and has filed a whistleblower complaint about the matter.) “[This was] one of my biggest frustrations when I was at Caltrans,” she says. The agency, she says, has “always gone to expansion and adding a new lane as the knee-jerk, first solution in the toolbox. Or, frankly, often the only tool in the toolbox. There are solutions that Caltrans should be considering and analyzing as real alternatives.”
‘There’s no way not to do the long term’
The interim projects do offer small but encouraging examples of a new phenomenon: blending transportation dollars and environmental dollars in the Bay. The benefits are potentially more money for both, and some protection from wild political swings. The Tolay Creek Bridge widening project, for example, is getting $50 million from a state transportation climate adaptation program (LTCAP) and $20 million from a Department of Transportation PROTECT grant to “ensure surface transportation resilience to natural hazards including climate change [and] sea level rise.” According to Toms, the transport agencies are “beginning to see the benefit, from a financial standpoint, of integrating these kinds of projects into their overall project planning.”
For now, those funds are secure, and the team is moving forward—although the specter of freezes and permitting delays still floats in the background. It helps that about 90 percent of the committed funds for the near-term Sears Point to Mare Island Improvement Project is funded by state or local dollars, not federal ones.
The long-term vision is still many years and billions away, but among the Resilient 37 participants I spoke to, there’s a feeling of cautious, gritted-teeth optimism.
“There’s no way not to do the long term. The only way we don’t do the long term is if we give up State Route 37,” said Weisman, who is keenly aware that the near-term projects do not buy the highway infinite time. “If we intend to keep State Route 37 operating as the east-west corridor connecting the North Bay, it has to be through a long term causeway.” Otherwise, we’ll say goodbye to the corridor forever. “It will be overwhelmed by rising Bay waters.”
Sea level rise waits for no man.
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The ghost of SR 37 past
Even if the causeway is successfully permitted, funded, and built, one big question remains: how do you get the old road out?
The new highway has to be constructed next to the existing one, to allow traffic to continue during the no-doubt-lengthy construction process. If the carcass of SR 37 is left behind, the potential for wetland connectivity will be lost. By the time the Bay fully overtops the highway and flows into the San Pablo Baylands, it will be too late for wetland to reestablish. “Is there a chance of a potential outcome where the existing road was to stay there? Absolutely,” says Fernandez, of the Regional Water Quality Control Board. But he adds that the project will be legally required to offset the environmental impacts of installing all the concrete piles that the causeway will sit on. “One source of mitigation would be to remove the existing road,” he told me. “So there’s a built-in incentive, if they can build the causeway, to remove the road.”
Ward-Waller is not so optimistic. “Removing that roadway and trying to get rid of all that contaminated soil that has had years of exhaust and oil going out into it would be a massive cost,” she says. “If it adds a billion dollars to what’s already a $10 billion project,” she says, it’s unlikely to come to fruition.
Weisman, of MTC, acknowledges that the old road is a looming unknown. But it’s too early to cost it out. “Any answer I’d give to you today would be a bad answer,” she says. “That will happen after the causeway is completed. What the costs are, what are the realities on the ground? I can’t fathom it. That’s something for the people who are on the program in about a decade, decade and a half.”
It’s the kind of massive, open-ended question that can quietly derail the project’s environmental ambitions. Weisman says, “We have to try to find a way to develop a project that is a big vision in terms of being multimodal, ecologically friendly, that really provides that connectivity, makes the right connections to land use and the community’s movement patterns, and that only costs as much as it as it needs to.” She’s clearly weighing all the elements, but it’s not hard to imagine some slipping through the cracks as timelines stretch and budgets tighten. That’s why the final chapter of SR 37 deserves just as much scrutiny as the first. If the old road stays in place, the ecological benefits, the big restoration wins, could vanish.
There might be a middle path. Toms imagines a gradual decommissioning process: knocking holes through the old highway to allow the tides passage, then adapting the remainder to new purposes as the sea rises. In this vision, the original SR 37 could become an innocuous, porous ghost, slowly reclaimed by wetlands that are weathering higher seas. “Maybe, for a decade or two, you’ve got a cool trail,” she said, “and then nature floods it.”
Or, maybe, the dream of wetland restoration gets stranded behind moldering concrete, trapped by the infrastructure it was meant to outlast.
This reporting was supported by the March Conservation Fund.
