HERMON – Maine State Police on Sunday continued their investigation into the cause of a one-car crash in Hermon that killed two women – the first traffic fatalities of the busy Labor Day weekend.

Maryellen Dean, 45, of Levant and her 26-year-old passenger, Alisha Andrews of Corinth, were eastbound to Bangor on Route 2 Saturday when their car left the road and struck a tree about 5:35 a.m., according to Maine State Police Trooper Forrest Simpson.

The women, neither of whom was wearing a seat belt, were going to work, but had apparently been running late as they were scheduled to start work at 5:30 a.m., Simpson said.

Simpson said Sunday he was thus far “pretty baffled” by the cause of the accident, which happened between the New Boston and Cold Brook roads.

“There was nothing out of the ordinary,” said Simpson, noting the absence of skid marks on the dry roadway.

But Simpson did say unused seat belts likely contributed to the seriousness of the crash.

“If people could only see these things firsthand, they wouldn’t think twice about [wearing seat belts],” he said. “I’ve seen a lot worse accidents with seat belts where people have been OK.”

Elsewhere in New England, a Brewer man and his as-yet unidentified passenger were seriously injured Sunday after a crash in the breakdown lane of I-95 north in Boxford, Mass.

Kevin Jowers, 32, of Brewer and his passenger were taken to Boston-area hospitals after a pickup truck crashed into their parked car.

The pickup truck’s driver, Richard Tanzella, 66, of Byfield, Mass., was killed in the crash.

Back in Maine, the Hermon accident was the first fatality on the state’s highways this three-day Labor Day weekend, which marked the end of the busiest summer ever on the Maine Turnpike.

Volume on the Turnpike in June, July and August exceeded levels for each of the same months a year ago.

Officials said more than 17 million vehicles traveled on the turnpike during this year’s three-month period.

Traffic was up 2.6 percent in June and 2.8 percent in July, with August traffic on pace to finish 3.9 percent above last year.

Heading into the Labor Day weekend, the American Automobile Association predicted that 32.7 million Americans would be on the road. That would be down from 33 million last year.

Airline travel was expected to dip by 300,000 to 3.8 million.

The Maine Turnpike carried a record volume on Aug. 9 when 231,000 vehicles used the highway, officials said. That topped the previous record of 222,000 recorded Aug. 17, 2001.

The Associated Press contributed to this report.