Three people were killed when the vehicle they were in rolled over early Saturday in Acadia National Park.

A fourth person survived the crash and was being treated at nearby Mount Desert Island Hospital in Bar Harbor, according to the National Park Service.

The accident occurred on the Park Loop Road around 3 a.m. It’s not clear what caused the crash, but by the time emergency personnel arrived, the three were already dead.

None of their names were being released pending notification of family members.

Investigators spent time at the scene Saturday trying to reconstruct the accident and closed the one-way section of Park Loop Road for several hours. It reopened about 8 a.m., according to park spokeswoman Christie Anastasia, who provided no further details.

The Park Loop road is the most heavily traveled part of Acadia and includes several popular stops such as Sand Beach, Thunder Hole and Jordan Pond.

It wasn’t clear exactly where the crash occurred on the 27-mile Park Loop Road, which begins at the Hulls Cove Visitor Center and turns into a one-way road about 2 miles in. There is a ranger station located prior to Sand Beach, where motorists must pay a fee if they haven’t already purchased a park pass, although that would not have been staffed at 3 a.m.

The accident remains under investigation and will involve the Park Service, the Bar Harbor Police Department and the Hancock County Sheriff’s Department.

The last accident in Maine that claimed at least three lives was in March, when three people were killed in a head-on crash in Westbrook that was attributed in part to black ice.

Traffic deaths are up 24 percent from last year, according to the Maine Department of Public Safety. Prior to this weekend, 105 people had died on Maine roads in 2019, compared to 84 during the same period in 2018. The total for 2018, 140, was among the lowest in decades.

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