An underground “utility corridor” carrying Michigan’s Line 5 pipeline and transmission cables across the Straits of Mackinac could prevent accidents but also cost at least half a billion dollars and take seven years to build.

The Michigan Pipeline Safety Advisory Board will hear a presentation Monday by a consultant who developed the concept with an engineering class from Michigan Technological University. The estimated price tag: $570 million.

As the debate over Line 5’s future continues, pipeline supporters have pointed to a tunneling option to ensure its operation while environmental groups have called for permanently closing the pipeline. The 15-member, governor-appointed board was created in 2015 to make recommendations on various pipeline issues, including Line 5.

The 21-foot-wide utility corridor could include not just Line 5 but also electric transmission cables and open spaces for vehicles to service the infrastructure if needed, according to the Michigan Tech study.

The $570 million construction cost does not include the “full picture” of engineering, permitting and other overhead, said James Morrison, the consultant who helped oversee the study.

An alternatives analysis last year gave a preliminary look at what it would take to build a tunnel for Line 5 beneath the Straits of Mackinac. (A risk analysis on the pipeline led by Michigan Tech researcher Guy Meadows is also ongoing.)

The tunneling idea has been roundly criticized by environmental groups, but the Snyder administration has expressed interest in the possibility, particularly after an anchor-strike incident last month that dented Line 5.

“Assuming studies show a tunnel is physically possible and construction would not cause significant environmental damage, the Governor will move to require Enbridge to construct the tunnel and decommission the existing Line 5 that runs under the Straits of Mackinac,” the administration said last month.

Morrison, who said the Michigan Tech team operated independently of the Pipeline Safety Advisory Board, said the alternatives analysis gave an incomplete picture of a potential tunnel.

“Whoever put it together had a concept but didn’t understand how to build a tunnel,” he said. “This could be an open utility corridor that you can reroute all of these utilities through.”

However, open questions and challenges remain, such as who might own, operate and pay for the tunnel. Morrison also said the geology of the subsurface where the tunnel might be built is not fully understood.

“One of the biggest problems is no one has drilled a hole in the middle of the Straits to confirm we don’t have a big fault running through there,” he said.

There is also political uncertainty. A statewide election in November will bring a new governor and attorney general whose position on Line 5 would likely chart the pipeline’s future. While Republican candidates, including Lt. Gov. Brian Calley and Attorney General Bill Schuette, have expressed support for tunneling, leading Democratic candidates for governor and attorney general have called for closing Line 5. In a televised debate Wednesday, Schuette stated his support for building the “utility corridor.”

Liz Kirkwood, executive director of For Love of Water, says a tunneling option may appeal to engineers but does not capture the range of ecological concerns around Line 5, which spans the Upper Peninsula and most of the Lower Peninsula.

The “peril” of responding to the recent anchor strike incident — which severed transmission cables and dented Line 5 — with tunneling, Kirkwood said, is “it fails to fundamentally analyze and ask the right question: Do we need this pipeline in Michigan? Not only does it threaten the Great Lakes, but also 245 other water crossings.”

The Michigan Tech study will help inform the Pipeline Safety Advisory Board about the feasibility of tunneling beneath the Straits, but it’s unclear how the findings may be used. “Hopefully presenting it will give (the idea) some legs and get interest for further study,” Morrison said.