A six-justice majority of the Michigan Supreme Court vacated the state’s siting approval for Enbridge’s Line 5 tunnel on July 31, reversing the Court of Appeals and sending a project that has been in permitting since 2018 back to the Public Service Commission.
The ruling landed less than three weeks after two other Michigan agencies issued their own permits for the same project. That timing tells you how these approvals actually work. They aren’t a sequence, they’re parallel tracks, and any one of them can stop the job.
The specific error the court found
The commission approved the project in December 2023. The court held it failed to properly apply the Michigan Environmental Protection Act, and the flaw was methodological rather than substantive.
Writing for the majority, Justice Elizabeth Welch said the commission must “compare the project and its alternatives on a consistent basis.” It hadn’t. The commission analyzed greenhouse gas emissions across the whole pipeline system, then limited its oil spill risk analysis to only the four-mile replacement segment. Two different boundaries, one comparison, and the court said that made a reasoned choice among alternatives impossible. The full opinion runs through the reasoning.
The commission must now also determine whether the replacement would be the proximate cause of Line 5’s continued operation and the environmental effects that follow, and separately evaluate impacts on public trust resources including fishing and navigation.
Why the alternatives-analysis point travels
Strip out the pipeline politics and what’s left is a rule about how agencies build records, and it applies well beyond this project. Any major infrastructure approval weighing a project against a no-build or alternative-route option has to define the analytical boundary the same way for every option on the table.
That’s a discipline problem in environmental review generally. It’s tempting to draw a wide boundary where a project looks good and a narrow one where it doesn’t, and the larger the program, the easier that is to do without noticing. Michigan’s court just made it reversible error at the state level.
Where construction stands
The approved design replaces two existing 20-inch pipelines with a single 30-inch line inside a concrete-lined tunnel bored through bedrock below the Straits of Mackinac lakebed. Enbridge selected Mackinac Straits Partners, a joint venture of Barnard Construction Co. and Civil and Building North America, to lead construction in 2024, with Arup as lead design engineer. Excavation hasn’t started.
The ruling doesn’t touch the wetlands and submerged-lands permit from Michigan EGLE or the threatened-species permit from the DNR, both issued July 15. It vacates only the commission’s Public Act 16 siting approval. Construction still needs that, plus an EGLE wastewater discharge permit, EGLE sign-off on mitigation plans, and a pending Army Corps of Engineers permit.
The 2018 cost estimate was around $500 million. An outside analysis cited by ENR put it past $750 million by 2022, and nothing since has made tunneling cheaper. No timetable has been set for the commission’s renewed review. Enbridge spokesman Ryan Duffy called the ruling “unfortunate” for the delay it adds.
For a contractor holding a position on a job like this, the lesson is old and expensive. A signed construction agreement is not a start date. Set it against a tunnel whose approvals are settled, like the Ohio River Tunnel, and the difference in carrying cost is the whole business.