LYNN – An unidentified man is said to have suffered severe head trauma after being struck by a northbound MBTA commuter rail train Thursday evening at Central Square station.The accident happened around 5:30 p.m., where a train on the Newburyport-Rockport line struck the victim, pinning him underneath. Police, fire and medical crews rushed to the scene and found a sneaker smashed underneath one of the train cars, followed by the victim a few yards away, bloodied, but still breathing.Frantically working to free the victim, crews pulled him out within minutes and rushed him to a waiting helicopter, which airlifted him to Beth Israel Hospital in Boston.Joe Pesaturo, spokesman for the MBTA, said the investigation is under way, but declined to release the victim’s name or extent of his injuries as of 9 p.m. Buses shuttled customers between the Lynn and Salem stations as a result of the accident, causing significant delays during the evening commute.A witness said the man was on the tracks and tried to jump out of the way of the train, but was unable to in time.Lynn Police Chief Kevin Coppinger shook his head in amazement and said the victim is “lucky to be alive.””It was close quarters, but we had access under the train (to free the victim) and got him out,” he said. “It was a good team effort.”About a month ago, MBTA General Manager Richard Davey visited The Daily Item and said 20 new rotating security cameras and surveillance warning signs would be installed by December in the commuter parking garage on Broad and Market streets.The cameras, signs and stepped-up day and evening patrols are the latest additions in an ongoing MBTA effort to improve safety in the block-long, six-story garage, where a woman was raped in June while in an elevator.