In a 6-1 decision released July 31, the court vacated the Michigan Public Service Commission’s (MPSC) approval of the proposed tunnel beneath the Straits of Mackinac and ordered regulators to take another look at the project’s environmental impacts.

Tunnel plan loses approval – for now

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The ruling doesn’t kill the tunnel project. Instead, it sends the case back to the MPSC, saying regulators didn’t fully do their homework before approving it.

The proposed project would replace the aging dual pipelines resting on the lakebed with a new pipeline housed inside a concrete tunnel beneath the Straits. The existing underwater pipelines would then be retired.

Court says environmental review wasn’t thorough enough.

The Michigan Supreme Court said the MPSC made three major mistakes. They erred by failing to consider whether building the tunnel would effectively extend Line 5’s operational life, potentially resulting in additional environmental harm.

Second, they said the MPSC compared alternatives inconsistently, making it impossible to fairly determine whether the tunnel project was the least environmentally harmful option. Third, the commission failed to analyze how the project could affect public trust resources, including the public’s rights in Michigan’s Great Lakes.

The court also ruled that environmental decisions under Michigan’s Environmental Protection Act must receive independent judicial review, rather than courts simply deferring to an agency’s conclusions.

Project delayed, not dead.

Supporters of the tunnel project argue it is the safest way to keep energy flowing while removing the existing pipelines from the lakebed. Opponents counter that any project extending Line 5’s life increases environmental risks.

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Enbridge spokesperson Ryan Duffy addressed the recent court decision in a statement to Bridge Michigan by saying, “One thing remains unchanged. We are fully committed to the safe and responsible operation of Line 5, incorporating enhanced safety measures in the Straits and continuing to safeguard Michigan’s natural resources now and for future generations.”

The decision adds another chapter to Michigan’s long-running legal and political battle over the pipeline. It also comes as the Whitmer administration continues fighting Enbridge in court, while the Trump administration recently filed a brief supporting the pipeline’s continued operation, prompting Michigan Democratic Governor Gretchen Whitmer to accuse the federal government of siding with “big oil.”