LANSING — M-185, roughly 8 miles long, is the only state highway in Michigan that does not regularly allow automobile traffic.

Most of the road is within, and is maintained in cooperation with, Mackinac Island State Park. The Michigan Department of Transportation invested about $6 million this year to repair high-water and wave erosion damage on the shoreline along M-185. Roughly 4 miles of the highway around the island sustained severe damage that escalated in fall 2019 and winter 2020.

“In 2020, it was a disaster out here,” said Steve Brisson, director of the Mackinac State Historic Parks in a news release. “The high lake levels were eroding the road into the water. Large chunks of it were washed away; the rest of it was often covered in boulders.”

This year’s project represented the third and final phase of road work after earlier emergency repair projects were completed. The work was designed to restore a safe pavement surface on M-185 and mitigate future erosion damage.

“We had to come to a decision,” Brisson said. “We either had to let the road go or do what MDOT did here. And it’s a remarkable job, and this is what it will take to preserve this remarkable roadway.”

The project, which began in May, repaired and upgraded armor stone along M-185, primarily along the eastern and northern shore of the island. Work also included pavement repairs to previously washed out and damaged roadway. Pavement markings will be painted on the road next year as part of a region-wide painting contract.