PITTSBURGH (KDKA) — The Port Authority’s light rail service resumed running early Monday before the morning rush hour.

It was the first time trains had run past Wood Street since a derailment Friday night injured three people, sending one to the hospital.

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Maintenance work was being done on the T north of the Gateway T station, so all trains were running on the southbound tracks at the time of the accident.

The southbound train had just left the Gateway T Station when it approached the switch over point. There was another train waiting on the northbound track for the T to pass so it could cross over and continue to the North Shore.

Port Authority spokesman Jim Ritchie says: “There was a signal violation and that’s very much like a traffic signal that you see on the road. There was a red light and a green light, and we do know the light rail vehicle went beyond the red signal. When it did, it moved into a switch change in the track, but the switch hadn’t fully moved into place yet, so the vehicle derailed.”

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As it left the tracks, the T was momentarily pointing towards the waiting train, giving people on board the impression they were going to be in a head-on collision. Instead, the rail car hit the center concrete pillar and was knocked back into the area of the southbound track.

The rail car was seriously damaged, and repairs to the tracks and rail infrastructure were not completed until late Sunday.

The investigation will continue with a few of the train’s black box and radio communications to try and determine where the mistake was made that allowed the train to run the red signal and derail.

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