The National Transportation Safety Board has released details of an investigation regarding a MARTA incident that injured an employee.

The incident occurred on Oct. 19 when a northbound MARTA train struck the employee who was performing maintenance work on train approach lights about 280 north of a tunnel exit between the Arts Center and Lindbergh Center Stations in Atlanta. The report adds that the employee suffered a below-the-knee amputation as a result of the strike. At the time of the accident, visibility conditions were clear

Investigators say the maintenance crew consisted of a watchman and three roadway workers and was tasked with repairing nonfunctional train approach lights. The maintenance crew was using several forms of protection, including inspection clearance, which notifies train operators of maintenance activities, but does not prevent the trains from entering the work area at track speed.

NTSB also says the maintenance crew was using a form of protection called watchman lookout, in which a watchman is assigned who is responsible for warning the maintenance crew of approaching trains. Also, the maintenance crew was using train approach lights that are activated when a train was detected on the track circuit. At the time of the accident, two employees were actively engaged in repairs alongside the watchman lookout. A fourth employee was in the train control room preparing to de-energize a relay to help identify the malfunctioning lights and possible oncoming trains.

According to the NTSB, the watchman said that he was focused on taking apart a light when the train exited the tunnel, and stated that he had presumed that the train alert lights that were activated at the time of the incident were from the testing the fourth worker was performing in the train control room.

NTSB investigators say while on scene, they inspected equipment, signals and track; performed sight-distance observations; and reviewed inward- and outward-facing image recorders, event recorders, radio communications, and surveillance cameras. The NTSB also reviewed MARTA’s policies and procedures and completed interviews with the train operator and the members of the maintenance crew.