Marin County and the North Bay could see the worst traffic delays in the Bay Area as highways become more prone to flooding, according to a new Stanford University study.
Published this week in the Science Advances peer-reviewed journal, the study assessed how a combination of sea-level rise, tides and storm surges in the next 20 years would affect the Bay Area’s existing traffic jams if left unaddressed.
While the North Bay doesn’t have the most flooding compared to other areas, the flooding occurs at critical connection points where few if any alternative routes exist, said study coauthor Jenny Suckale, an assistant geophysics professor at Stanford.
That’s bad news for Marin.
“It’s very sparse,” Suckale said. “You have (highways) 101 and 37. That’s about it. You don’t have a lot of alternatives. The other thing too is a lot of the roads in the North Bay tend to correlate with topographic lows.”
Other areas such as the South Bay are expected to have much more flooding, but models show that will have minimal effects on traffic flow because of their dense road networks, Suckale said.
The study assessed where commuters would experience 30 minutes or more of traffic delays at a 12-inch water level increase in the next 20 years. At 12 inches of elevated bay waters, more than half of commuters in areas such as San Rafael, San Anselmo and Novato would experience these long delays.
The models are based on traffic data by the Metropolitan Transportation Commission, employment and commute data from the U.S. Census Bureau and sea-level rise projections from the San Francisco Bay Conservation Development Commission.
Suckale said a common sentiment among communities that aren’t close to the coasts such as Santa Rosa did not feel they would experience as acute a traffic delay compared to areas more prone to flooding. However, the study found these areas would be some of the hardest hit by traffic delays, especially affecting workers who are already making long commutes.
“The North Bay, in particular, will suffer very significant commute delays even though they don’t have most of the flooding,” Suckale said. “Traffic is one of those ways in which we are very much connected, particularly in the Bay (Area). The Bay (Area) is probably even more than other urban areas because of just a few traffic chokepoints such as the bridges.”
Sea level projections are estimated to rise about 11 inches by 2050, according to the Bay Conservation and Development Commission, with storm surges and high tides exacerbating flooding issues.
For Highway 37, which is already flood-prone and is located on a sinking roadbed, a 1-foot sea level increase would result in frequent flooding along the section near Novato Creek, according to studies by MTC and the University of California at Davis. At 3 feet of sea-level rise, which projections show could occur by 2100, all segments of the highway would face permanent inundation.
The study illustrates the vulnerabilities of the Bay Area’s transportation network, said MTC spokesman John Goodwin. An outline of a regional long-term planning document called Plan Bay Area 2050 by MTC and the Association of Bay Area Governments prioritizes sea-level rise adaption projects including raising sections of highways 101 and 37 in Marin County.
“Because U.S. 101 really is the only north/south corridor through the county, this magnifies the flooding risks around 101 and its interchanges in Marin City, Corte Madera and central San Rafael,” Goodwin wrote in an email. “And then of course, you have the myriad vulnerabilities of Highway 37, which are not just a 20-year concern but a right now concern.”
As part of its Marin Bay Waterfront Adaptation Vulnerability Evaluation, the county has assessed how sea-level rise will impact not only transportation corridors but also transit and emergency services such as fire stations and hospitals. Coastal flooding is also a concern for the Interstate 580 and Highway 101 interchange as well as Highway 1.
“Marin County is a peninsula and we know that there are limited routes in and out of the county,” said Chris Choo, county principal watershed planner. “Sea-level rise will impact the entire county since roads bring workers, food and the ability to go about daily life. No matter where someone lives in the county, they likely need the transportation network to function and localized flooding can often lead to countywide impacts.”
The challenge, Choo said, is how to prioritize and fund many of these major projects, especially during the current state of the economy.
Anne Richman, executive director of the county’s traffic congestion management agency, the Transportation Authority of Marin, said that while she has not fully reviewed the Stanford study, the overall findings are not completely surprising based on past studies by the county and Caltrans.
While there are larger regional projects being considered to address the physical roads, Richman said reducing greenhouse gas emissions from transportation — the largest source in the Bay Area — by promoting transit, electric vehicles and alternative commute options must continue.
“It definitely highlights the importance of continuing to work on those projects that have already been identified,” Richman said.
The far-reaching impacts caused by localized flooding cannot be addressed through a piecemeal approach, Suckale argues.
“It’s important to keep in mind that this is a regional problem, we need regional solutions,” Suckale said. “You can’t do it piece by piece.”
More information about the study can be found at stanford.io/2F4v007.
