Future of State Route 37

The future of State Route 37 and historic baylands depends on funding and political will 

By Kate Powers

Can the reconstruction of State Route 37 (SR 37) into an elevated four-lane causeway be accelerated in time to not  only reduce congestion and protect the highway from sea level rise, but also for tidal wetlands to re-establish before inundation? 

That is the billion-dollar question. 

Much has been written of late about SR 37, the North Bay highway that runs across the historic baylands of Marin, Sonoma, Napa and Solano counties. While the highway serves much of Marin’s workforce that commutes from affordable homes in Solano County to well-paying jobs in Marin, it regularly experiences substantial peak period congestion due to a 10-mile stretch from Sears Point to Mare Island that narrows from four lanes to two, one lane in each direction. It currently has no transit options or carpooling incentives. In addition to travel delays, the highway experienced closures (in 2017 and 2019) due to flooding and is subsiding. The California Department of Transportation (Caltrans) predicts that, due to rising sea levels, large stretches of SR 37 will be under water by the year 2040. 


A sea level rise adaptation “Ultimate Project” 

The 21-mile highway has been the focus of many concurrent studies and planning efforts over the last several years. The most recent, Caltrans’ Planning and Environmental Linkages (PEL) Study, is planning for a sea level rise adaptation Ultimate Project. To date, the study has evaluated almost a dozen potential re-alignments and transportation alternative solutions using a broad range of environmental, traffic, design, and feasibility criteria. The PEL study is expected to conclude by year end. 

At a recent Resilient SR 37 Policy Committee1 meeting, Caltrans presented the PEL preferred alternative – a mostly elevated causeway along the current right-of-way. The causeway would touch down only at a couple of ridgeline elevations. The preferred alignment best meets PEL’s Purpose and Need, and avoids “new location impacts” to wetlands, critical habitat, and/or the bay floor. The causeway’s design will accommodate bicycles and pedestrians on or near the structure; include access to locations on both sides of the facility through redesigned interchanges and intersections; and allow for removal of fill of the existing roadway. Current estimates for the Ultimate Project are between $6 and $8 billion. Opportunities to lift the existing railway out of the Baylands and possibly co-align it with the causeway are also being considered. Caltrans will update the public on the PEL process at a virtual meet- ing on Wednesday, September 14, 5:30 –7 pm. 


The clock is ticking 

The landscape over which SR 37 travels is comprised of a mosaic of historic baylands all along the northern edge of San Pablo Bay. While much of San Francisco Bay’s tidal marsh- es have disappeared, many of the North Bay’s wetlands have slowly but deliberately been acquired or protected and are being brought back to life. The San Pablo Baylands (Baylands) are unique in restoration opportunities due to the patchwork of large parcels in the hands of a relatively few public, private, and nonprofit landowners. Included in the historic Baylands are Petaluma Marsh, the largest prehistoric tidal marsh remaining in California; and seven former salt production ponds, now managed to provide habitat for shorebirds and dabbling ducks. The Baylands continue to be a major destination along the Pacific Flyway. 

The most critical time for restoring the Baylands is now. By 2030, Highway 37 will be subject to frequent flooding. Tidal marshes that are well established will more likely flourish and provide ongoing benefits, including habitat resilience, carbon sequestration, and flood protection as sea levels rise. 


The impacts to wetland restoration from Interim projects 

Two concurrent interim projects are also in progress. They are considered temporary, as neither are designed to ultimately address sea level rise. One, a Flood Reduction Project, proposes to elevate the segment of SR 37 from US 101 to SR 121 and to reconstruct the segment’s bridges to address near-term flood- ing. Preparation of that draft environmental document was paused until the PEL process draws to conclusion. Construction is planned to begin in 2027 depending on funding availability. 

A second project that is further along in the planning process, the Sears Point to Mare Island Improvement Project, is receiving lots of attention. Its purpose is to relieve congestion by widening the roadbed and the Tolay Creek Bridge (one of the worst traffic areas in the corridor); increase vehicle occupancy by providing a commuter/transit express lane; and address roadway subsidence by raising pavement. A draft environmental impact report was released in January. All of the “build” alternatives widen the roadway and would require acres (thousands of truckloads) of in-water and upland fill and additional impervious surface that would impact sensitive marshlands, and cause loss of wetlands communities, and non-listed special status, threatened, and endangered species according to the report. Some alternatives would require acquisition of small portions of San Pablo Bay National Wildlife Refuge. Comments on the draft were due February 28. 

If the Sears Point to Mare Island interim project is permitted, the proposed mitigation for the project is to lengthen Tolay Creek Bridge which would broaden the channel and enable ecological restoration of Tolay Creek—a time sensitive and critical restoration priority for the Baylands. Additional mitigation could include restoration of a roughly 700-acre strip marsh along the segment, south of the highway. The strip marsh is important natural infrastructure that protects the highway from inundation and provides critical habitat. Construction for the interim project is planned to begin in 2025 with an estimated price tag of $430 million, though permitting hurdles for mitigation may increase delivery time and expense. (The cost to remove the added fill and asphalt from the interim project, once an Ultimate Project causeway is constructed, is not included in the estimate.) 



In November 2020, the Biden administration announced it would prioritize “shovel-worthy” projects for federal funding. Shovel-worthy are long-term solutions to complex and ex- pensive critical infrastructure challenges. They often don’t qualify for “shovel-ready” funds. In 

November 2021, President Biden signed the Five-year Bipartisan Infrastructure Law (BIL). It’s expected to fund a “once-in-a-generation” investment in U.S. infrastructure and includes $110 billion in new competitive grant funding for roads, bridges and major projects. 

In addition to federal competitive grant opportunities, California will receive $10 billion in new (additional to existing) federal formula funds for transportation over the next 5 years. The state is poised with a $100 billion state budget surplus and California’s Five-year Infrastructure Plan to leverage and maximize federal funds. During the 2022-23 State Bud- get process, the Bay Area Caucus, including Senator McGuire and Assemblymember Levine, submitted a funding request to the legislature that included $6 billion for SR 37. To date, the 2022-23 state budget has committed little more than $100 million for the Interim and Ultimate Projects combined. 

The Metropolitan Transportation Commission (MTC) is pursuing state and federal competitive grants for the Sears Point to Mare Island interim project. However, SB 1050, State Senator Dodd’s tolling legislation that would have authorized high-occupancy toll lanes or other toll facilities on SR 37, died in Appropriations Committee. The toll revenue would have provided the necessary local match for project funding. 


Accelerating shovel-worthy to shovel-ready 

While transportation agency partners agree that SR 37 will need to be replaced before 2040, and that the highway needs to be elevated. MTC has argued that the current interim projects are critical initial phases of the Ultimate Project. Several stakeholders fail to agree, asking Caltrans to focus on accelerating the Ultimate Project, fearing the longer the wait, the more it will cost. 

Congressman Jared Huffman, who serves on the House Transportation and Infrastructure Committee and Select Committee on the Climate Crisis, has championed shifting SR 37’s priorities to building the causeway. He’s ex- pressed concern that interim widening could politically undermine chances for securing federal funds for the Ultimate Project. 

Readying shovel-worthy projects for delivery not only requires funding. Preparation for 

environmental assessment and permitting can require thousands of hours and cost millions of dollars. The extent to which regulatory and permitting agencies work together to prioritize review of critical infrastructure projects, the less costly and more promptly they will be built. 


Coalescing political will 

The State Route (SR) 37-Baylands Group1 is composed of practitioners, and others, interested in and responsible for the conservation, management, and restoration of the San Pablo Baylands. As a participating organization, MCL signed on to the Baylands Group’s SR 37 Position Paper. It: 

• Supports building a causeway in the cur- rent SR 37 right-of-way and accelerating the Ultimate Project to enable timely flood risk management and wetland restoration; 

• Emphasizes the self-mitigating nature
of the Ultimate Project (as opposed to mitigations that would be needed by the proposed interim projects) and recent regulatory agency policies that help “cut the green tape” to accelerate implementation of multi-benefit, climate change adaptation projects. This increases the likelihood that the Ultimate Project would move quickly through environmental compliance and permitting; 

• States SF Bay Regional Water Quality Control Board’s commitment to lead permit coordination of the Ultimate Project with the region’s other regulatory agencies including the US Army Corps of Engineers, US Fish and Wildlife Service, National Marine Fisheries Service, California Department of Fish and Wildlife, and the San Francisco Bay Conservation and Development Commission; and 

• Requests that all interim projects be low- cost, low-impact fixes, or serve as logical, substantial steps towards implementation of the causeway. 

With the restoration communities and regulatory agencies aligned, accelerating implementation of the Ultimate Project seems possible. It’s time to undo the damage from generations past, and to focus investment strategies on funding a shovel-worthy transportation and environmental win. Restoring the connections of wetlands to the San Pablo Estuary will serve both climate change adaptation and mitigation efforts, on a landscape scale. Opportunities like these are few and far between but they require combined and coordinated commitment for success. 


1 For info on SR 37 Policy Committee and the SR 37 Baylands Group, see article in MCL’s Jan-Feb 2022 newsletter. 

 For history of San Pablo Bay, see John Hart’s “Highway to the Flyway” in July 2007 issue of Bay Nature magazine. 

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