Local transportation leaders heard from the experts that elevating Highway 37 above rising sea levels is financially possible—if travelers pay a toll.

The 21-mile-long highway runs from Vallejo to Novato through the Napa-Sonoma marshes. Estimated costs to elevate the road on a levee or causeway range from $1 billion to $3.4 billion in 2022 dollars, with costs rising in subsequent years.

On Wednesday, Jose Luis Moscovich of Project Finance Advisory Ltd. spoke to the Napa Valley Transportation Authority Board of Directors. His firm studied how an elevated Highway 37 could be financed.

“What you’re doing right now is the very first step in deciding if you’re just dreaming or if it is feasible,” he said.

The answer?

“You do have a potential project that’s feasible … if you toll,” he said.

A $6 toll could pay for a $1 billion project. A $7 toll could pay for a $2.6 billion project, he said.

Another option is to do no tolling and pay for an elevated Highway 37 through traditional, public highway funding sources. Moscovich said that could delay the fix until 2088. A U.C. Davis study predicts much of the road will be underwater by then.

“There’s more water in your future and this road needs solutions,” Moscovich said. “Regardless of what you think about climate change, sea levels are rising.”

Regional transportation planners take the predictions seriously and have looked at possible Highway 37 solutions for months. Napa, Solano and Marin counties, the state Department of Transportation and Metropolitan Transportation Commission are among the parties involved in the discussion.

The State Route 37 Policy Committee, of which Napa County is a member, hired Project Finance Limited as a financial adviser. County Supervisors Alfredo Pedroza and Belia Ramos and American Canyon Mayor Leon Garcia are on the committee.

Highway 37 may or may not run through a very short section of Napa County’s southwestern tip – the road is so close to the county line that maps vary on this. But regardless, Highway 37 affects Napa County.

Local officials expect that, should a toll become a reality, some people will take a detour to avoid it. That detour would bring more traffic to already congested Highway 29 and Highway 121 in southern Napa County.

“This is a tremendous burden for our highway system, which is very basic,” said Ramos, who also sits on the NVTA Board.

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Moscovich said this matter will be considered as the project takes shape and an environmental document is done.

“But the other option is to have full diversion when the road is flooded,” he said.

That happened this past winter during heavy rains, when a flooded Highway 37 closed for 27 days. Caltrans estimates about 40,000 drivers use the highway on an average day.

Elevating Highway 37 and widening the local section from two lanes to four lanes faces more than financial challenges. The road runs through wetlands that are home to plants and wildlife protected by the Endangered Species Act, such as the salt marsh harvest mouse.

The cheapest option under consideration at $1 billion is a levee road. A photo simulation shows what looks like an earthen dam or dike with a freeway running atop it and waters from San Pablo Bay lapping at its base.

Two versions of a causeway are under consideration. The $3.4 billion version looks like a twin of the graceful Imola Avenue bridge over the Napa River, but one that extends for miles.

NVTA directors held no extended debate on Highway 37 issues. They didn’t recommend whether to bring in a private developer or to have one toll for the entire 21 miles or toll various segments.

Wednesday’s session amounted to an update on a complicated project that is only beginning to take shape.

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Barry Eberling covers Napa County government, transportation, the environment and general assignments. He was worked for the Napa Valley Register since fall 2014 and previously worked 27 years for the Daily Republic of Fairfield. He is a graduate of UC Sa