An “intermittent anomaly” in the braking system of a light-rail car likely caused the 2017 crash on the Norristown High Speed Line in Upper Darby that injured 43 people, federal transportation safety regulators have concluded.

The National Transportation Safety Board reported the finding Nov. 10, apparently closing the book on an accident investigation that began Aug. 22, 2017, when car 155 failed to stop and hit the rear of an empty train car parked in the 69th Street Transportation Center at 12:11 a.m.

Shortly after, SEPTA reduced speed limits on the line as a precaution. The lower speed rules remain in effect.

The operator of car 155 applied the brakes properly, had no medical issues, and tests showed no drugs or alcohol in his blood, the NTSB said.

The agency did not identify any systemic concern with maintenance of the 26 cars on the Norristown line.

The fleet of N-5 rail cars, which went into service in 1993, has not had any significant mechanical defects, nor have the braking problems reappeared since the crash, said Andrew Busch, chief spokesperson for SEPTA. “We have not seen anything similar,” he said.

Forty-two passengers and the train operator reported being injured in the accident and were treated at area hospitals.

» READ MORE: Trains crashed at 69th Street despite safety protections (from August 2017)

In a preliminary report a month after the crash, the NTSB said there had been warnings of speed and slippery rails on the route shortly before the collision. It had been raining lightly.

SEPTA immediately lowered the line’s maximum speed limit from 70 mph to 55 mph and required trains to travel 45 mph or below while passing through stations. It also reduced the limit to 30 mph between Township Line Station and the 69th Street terminal, and dropped it to 15 mph approaching the station.

Now that the investigation is complete, Busch said SEPTA would review the speed limits but likely would keep them lower, at least on the southbound section between Township Line Station and 69th Street, which has two relatively steep descending grades.

Performance data recorders aboard car 155 “showed 10 wheel slides during the 45 seconds before the accident,” the NTSB final report says.

There had been similar slippage four days before the accident, the NTSB said. “On the night of the accident in wet weather, car 155 exhibited sudden intermittent and frequent wheelspin/slide events accompanied by substantial and unexplained reductions in acceleration and deceleration,” the final report said.

News researcher Ryan W. Briggs contributed to this article.