Enbridge is planning to replace a section of the pipeline, which runs underwater for 4 miles (6.4 km) through the Straits of Mackinac between Lakes Michigan and Huron, to address concerns Line 5 could leak.
The Michigan Public Service Commission (MPSC) approved Enbridge's siting application, finding there was a public need to protect the Great Lakes from the risk of an oil spill while also keeping the pipeline operating.
"There are no feasible and prudent alternatives to the replacement project pursuant to the Michigan Environmental Protection Act (MEPA)," the MPSC said in a decision posted on its website.
Calgary-based Enbridge still requires federal permits from the U.S. Army Corps of Engineers and construction is not expected to start before 2026.
The company first submitted an application to build the tunnel in 2020 to address concerns Line 5 could leak. The 70-year-old pipeline carries 540,000 barrels per day from Superior, Wisconsin, to Sarnia, Ontario, and is at the center of a long-running legal dispute between Enbridge and the state of Michigan, which says it should be shut down.
"With the MPSC’s decision, the Michigan agencies involved in the permitting process have given the go ahead for this critical project," Enbridge spokesperson Ryan Duffy said in a statement.
The decision was criticised by some environmental groups opposed to the project, who say it is not necessary to keep Line 5 running in a world aiming to transition away from fossil fuels to cleaner sources of energy.
"We are extremely disappointed in the commission’s actions today as they ignored warnings from safety and energy experts that a tunnel would continue to leave the Great Lakes and our climate at risk," said Bentley Johnson, from the Michigan League of Conservation Voters.
