The Michigan Public Service Commission has approved a controversial project to relocate a segment of Enbridge's Line 5 oil and natural gas pipeline from the bed of the Straits of Mackinac to a service tunnel beneath it.

The  2-0 vote on December 1 paves the way for the "Great Lakes Tunnel" project, intended to address concerns about the vulnerability of the aging pipeline.

"We are ready to begin work on this project," said Ryan Duffy, a spokesperson for Canada-based Enbridge Energy, in a statement, adding that the only remaining hurdle is a decision on their permit application by the U.S. Army Corps of Engineers.

The project is expected to begin in 2026, pending the Corps' environmental impact review. However, Enbridge has yet to select a contractor or finalize the route for the three-and-a-half to five-mile tunnel.

Commission Chair Dan Scripps, who voted in favor of the tunnel, described it as the "most prudent option" for replacing a portion of the dual pipeline.

Line 5 currently carries 540,000 barrels of crude oil per day from Sarnia, Ontario, Canada, to Superior, Wisconsin, with a portion of the route crossing the Straits of Mackinac, which connect Michigan's upper and lower peninsulas.

The commission also considered alternative transportation methods, such as trucks, rail, oil tankers, and barges. However, these options were deemed likely to increase environmental impact and spill risks.

Scripps identified anchor strikes as the most likely cause of potential damage to the 70-year-old pipeline, pointing to the 2018 incident where an anchor dented the pipeline's protective coating, highlighting the vulnerability of the existing system.

Environmentalists and Native American tribal representatives expressed concerns about the pipeline's continued operation. They emphasized the urgency of shutting down the pipeline entirely, citing the risk of a rupture even before the tunnel's completion.

Line 5 has been the subject of controversy for years. In 2018, Enbridge agreed with then-Governor Rick Snyder (R) to build a tunnel to house a new segment of the pipeline. However, current Governor Gretchen Whitmer (D) attempted to shut down the pipeline via executive order in 2020, but a federal judge blocked her action in 2023.

Similar efforts to shut down the pipeline by both Governor Whitmer and Michigan Attorney General Dana Nessel (D) were previously denied in court.

Although Enbridge has not yet updated the estimated cost of the service tunnel project, the 2018 plan shows the tunnel will be large enough to allow trucks to pass through for maintenance purposes, with Enbridge responsible for funding the construction, as stipulated in the 2018 agreement.

While the tunnel project has received approval from the Michigan Public Service Commission, it faces further regulatory hurdles due to concerns raised by environmental and tribal groups who advocate for the pipeline's full closure.