Caltrans workers divert traffic around a flooded area of Shoreline Highway near the Highway 101 onramp in Mill Valley during a king tide on Friday, Dec. 23, 2022. (Alan Dep/Marin Independent Journal)
The Transportation Authority of Marin is set to launch the county’s first study of sea-level rise impacts — and potential defense measures — on Marin’s transportation network.
The authority’s Board of Commissioners voted unanimously on Thursday to approve up to $550,000 for the estimated 18-month study, which is expected to be completed by late 2024.
Anne Richman, the agency’s executive director, said while Marin County government, Caltrans and other entities have conducted or are preparing their own separate studies on sea-level rise vulnerability in Marin and on local highways, she said this assessment will be the first to focus on roads, pathways and highways countywide as well as develop potential options for protections or adaptations.
“There is certainly a lot of interest in this topic right now,” Richman said Friday. “I’m really interested in getting into the options and project concept beyond just understanding where the vulnerable locations are and really starting to get into what communities can try to do about it in the future.”
The authority is Marin County’s state-managed traffic congestion management agency and administers sales tax and vehicle registration fee collection through Measures AA and Measure B. The Measure AA sales tax measure, renewed by voters in 2019, allots 1% of its revenue toward sea-level rise planning.
The study will be conducted by the multinational design and planning company, Arup Group, based in London.
Given other sea-level studies that have taken place or are underway, such as Marin County’s BayWAVE and CSMART studies as well as Caltrans’ study on state highway vulnerability, TAM board members questioned staff on how this latest study will differ from others.
“I’m concerned about doing a lot of duplication of efforts and having a product that comes out that hasn’t really coordinated with another agency’s work in the same exact area,” board member and Marin County Supervisor Katie Rice asked staff during the Thursday board meeting.
Staff said the new study will be coordinating with all local jurisdictions and agencies to include information from completed sea-level rise assessments and any projects underway. Areas such as Highway 37 that have already undergone significant review and are currently in the planning stages will not be included as part of the review.
“I expect we’ll reference it but not redo it,” Richman said.
The study will also not perform a deep dive into individual transit networks as the Measure AA fund is designated for local streets and highway projects, Richman said.
“We definitely do want to pay attention to transit where there may be co-benefits,” Richman said, adding that any in-depth study would need to be done by the individual transit agencies.
Part of the study will also look at potential adaptation measures or defenses that would not only protect local roadways and highways.
“I think we’re trying to look at potentially off-corridor protections that can add co-benefits to protecting our communities,” the authority’s planning manager, Derek McGill, said Friday.
Initial work on the study is expected to begin in May, Richman said.
