Caltrans details $1.6B plan for elevated Highway 37 causeway near Novato

The first phase of a massive plan to elevate Highway 37 to prevent regular inundation from sea-level rise is set to begin with an estimated $1.6 billion project in Marin.

Caltrans officials held a presentation recently on the agency’s plan to rebuild a 2.5-mile section of the 21-mile North Bay commuter route as an elevated causeway from the Highway 101 interchange in Novato to the Atherton Avenue exit.

The project would be the first in the agency’s plan to elevate the entire highway onto a causeway before the road connecting Marin and Solano counties becomes regularly inundated by rising sea levels, which Caltrans projects will begin in 2040.

At a public hearing on the proposal in Novato this month, Caltrans project manager Javier Mendivil said the project is needed “to incorporate resiliency on the corridor to the effect of sea level rise to 2130 and flooding from stormwater.”

The state agency plans to conduct the project in two phases, beginning by rebuilding the Novato Creek Bridge onto a 35-foot-high causeway by June 2029. The second phase, aimed for completion in 2049, would rebuild the remaining sections of the 2.5-mile portion of the highway as a 114-foot-wide causeway including a bicycle and pedestrian path.

The existing road will be removed after the project is completed in 2049. The total project cost is estimated to be nearly $1.6 billion, according to Caltrans spokesperson Matt O’Donnell.

The causeway plan, detailed in a draft environmental analysis released in late August, would include four 12-foot-wide vehicle lanes; two 10-foot-wide inside shoulders and two 12-foot-wide outside shoulders; and a 14-foot-wide bicycle or pedestrian path.

The two sides of the road would be separated by a 2-foot-wide median barrier. The bicycle path would also be separated from vehicle traffic by a barrier.

Caltrans plans to begin with the Novato Creek Bridge given its existing flooding issues, which have recently caused full highway closures since 2017 and headaches for tens of thousands of commuters.

Caltrans states that it would be able to maintain traffic on the highway for most of the first phase of construction, with traffic impacts expected to add 15-minute delays.

The agency plans to maintain four lanes of traffic by constructing a 1,000-foot-long median between the existing highway. Caltrans would divert westbound traffic onto the median first and would remove the existing westbound bridge. The median will then be widened by 30 feet, allowing Caltrans to divert eastbound traffic onto the median and remove the existing eastbound bridge.

Two weekend closures would be needed during the first phase, in which traffic would be rerouted onto city and county roads. The proposed detour route would divert westbound traffic onto the Harbor Drive exit and have traffic travel on Atherton Avenue before entering Highway 101.

The second phase of construction is also expected to cause up to 15 minutes of delay, based on existing traffic volumes, but could be increased due to planned closures of the Atherton Avenue on-ramps and off-ramps, according to Caltrans.

Some Marin officials and environmental organizations said they support the plan to elevate the highway given its environmental benefits and the existing flooding impacts.

Marin County Supervisor Eric Lucan, who serves on the Highway 37 Policy Committee, said the project “casts the vision for the reimagined Highway 37 corridor.”

Environmental organizations such as the Sierra Club, Marin Audubon and Marin Conservation League state elevating the highway will help to restore wetlands along the corridor that have been blocked from tidal influence by the berm the highway is built on.

The San Francisco Estuary Institute nonprofit group has previously stated that elevating the entire 21-mile corridor would result in the largest wetland restoration project on the west coast of North America.

“It increases flood protection upstream, it lets the rising water filtrate into the marsh, and sequestering carbon is important in keeping as many marshlands we have left,” said Marin Conservation League member Kate Powers.

Steve Birdlebough, transportation chairman for the Sierra Club Redwood chapter, said one of his main concerns with the proposal is that the Marin section will not include a dedicated carpool lane as is proposed by Caltrans for the 10-mile section of highway between Sears Point and Mare Island. Birdlebough said that this could lead to traffic jams heading toward the Highway 101 intersection and would disincentive carpooling and transit commutes.

“This isn’t going to be a problem in the first five years of operation but by 2045 it will be a significant problem,” Birdlebough said. “And it will mean that anybody who is driving from Vallejo to a job in San Rafael is just going to be just as backed up and take as long as it does today.”

Caltrans is accepting public comments on its draft environmental analysis of the project until 5 p.m. Oct. 8. Comments can be submitted by email to SR37FloodProject@dot.ca.gov or by mail to Caltrans District 4, Skylar Nguyen, P.O. Box 23660 MS-8B, Oakland, CA 94623.

A copy of the environmental analysis can be found at bit.ly/48znTpt.