The state of Michigan and Canadian company Enbridge Inc. signed an agreement under which the company would replace the Line 5 petroleum pipeline segment that crosses the Straits of Mackinac with a multi-utility tunnel beneath the Straits, according to an Oct. 3 press release from the Michigan Governor’s office. Enbridge agreed to bear the costs of construction – estimated to range from $350 million to $500 million – and operation of the tunnel for up to 99 years. The deal is subject to approval by the Mackinac Bridge Authority, which would own the infrastructure and lease space to Enbridge. Building on a November 2017 safety agreement, the new deal requires additional actions to expand safeguards along the segment. As part of the new measures, Enbridge must make at least $1.8 billion available to respond to potential oil spills. The 645-mile Line 5 transports up to 540,000 barrels a day of light crude oil and natural gas liquids underneath the Straits of Mackinac.