An option floated by the governor to replace the aging Line 5 pipeline across the Straits of Mackinac could take seven years and a half-billion dollars to construct, according to a research project by Michigan Technological University students.

The project examining the costs, risks and time of building a 4.1-mile-long utility tunnel in the Straits was presented this week to the Michigan Pipeline Safety Advisory Board at its May 14 meeting.

The idea behind the project: put all existing utility connections across the Straits of Mackinac into one underground concrete tunnel measuring 21 foot in diameter, thereby protecting the lines from hazards, containing possible spills and allowing better maintenance control.

The Michigan Tech students estimated a total cost of nearly $570 million. That figure doesn’t include pre-construction engineering and planning, owner management and overhead and profit.