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The state revealed Monday that it plans to raise the Deer Isle Causeway 4.3 feet higher to better withstand sea level rise and strong coastal storms.
Under the proposal, nearly a mile of the main causeway connecting Deer Isle-Stonington to Little Deer Isle and another, smaller one near the base of the Deer Isle-Sedgwick Bridge would be improved through a $22 million, two-year project. Of that amount, $12 million is federally funded by congressionally directed spending.
Portions of the work, which would wrap up in the fall of 2029, will limit the road to single-lane traffic, the Maine Department of Transportation said.
The release of the full plans and timeline are a step in the long-awaited project to rebuild the vulnerable road, which was temporarily closed in January 2024 after being flooded and covered with large rocks during a pair of historic storms. The causeway connects island residents to services, jobs, education and economic opportunities on the mainland, including for Stonington, the state’s top lobster port. Local officials have voiced concerns about it for years, even before those storms.
The aging Deer Isle-Sedgwick Bridge — another state-owned connection to the mainland — also worries residents. The state is starting to investigate options for that suspension bridge, according to its current work plan, but any major project there is likely far off.
The Deer Isle Causeway sees an average of 3,250 vehicles per day, according to state documents. That number is expected to increase to 3,580 by 2045.
When shorefront roads flood during strong storms, they are covered with water and debris, and the strength of the tide can cause bigger structural problems by destabilizing the road bed.
The causeway is one of multiple flood-prone roads that are the only connections between a Maine community and the mainland. Raising them are generally major infrastructure projects that small towns can’t afford alone.
Along with reconstructing and raising the causeways, the Deer Isle project proposal includes adding five-foot road shoulders, adding riprap to protect the road from future storms and managing access at various points along the causeway to make them more safe and visible.
The causeway would be raised up 4.3 feet, to a total height of 13.3 feet, according to an online presentation about the project posted by the Maine Department of Transportation this week. That’s 6 feet above the highest astronomical tide line.
The 13.3 foot estimate is about half a foot less what the department was predicting last year, when parts of the road were expected to be 13.8 feet or even higher.
The new elevation is “practical, feasible and responsive for the next 75-plus years,” according to the department — several feet above predicted sea level rise by the end of the century and higher than the water levels brought by the 2024 storms.
It should protect the roadway from a reasonable combination of sea level rise and future storm events, and has the potential to be raised again in the future, according to the presentation.
The causeway’s base layers will be rebuilt first — which will still allow the road to be open to two-way traffic — followed by building out the left and then the right sides of the road, closing it to one lane.
The department aims to start work in the fall of 2027 and finish it in the fall of 2029.
Comments and questions on the proposal will be accepted online through June 24. An in-person project information session is scheduled for the Deer Isle town office at 6 p.m. Wednesday.
