A mobile maintenance backhoe struck by an Amtrak train near Chester, Pa., on April 3 was authorized to operate on the rail tracks within a scheduled 55-hour maintenance window, according to a preliminary report of the incident by the National Transportation Safety Board (NTSB).

The Amtrak-owned backhoe was performing routine cleaning and ballast maintenance on an adjacent, deactivated track when it was hit head-on by the locomotive of a southbound 10-car passenger train traveling at 106 mph, just under the area’s authorized speed of 110 mph. Investigators say the engineer initiated an emergency-brake application after “seeing something” on the track immediately before the crash, which killed the backhoe operator and supervisor and injured more than 40 passengers.

Several passenger cars also were damaged by debris from the impact. Amtrak estimated total damages to be $2.2 million.

The report also notes that the area’s three other main tracks were intermittently taken out of service during the maintenance window, begun on the evening of April 1, to protect the backhoe as it performed its work. No explanation has been given as to why both the backhoe and the passenger train were occupying the same track.

Still to be determined is whether the passenger train’s positive train control (PTC) system was functioning properly at the time of the crash and whether all worker-protection measures were in place. Amtrak completed PTC installation along the Northeast Corridor last fall, following a deadly high-speed derailment in May 2015 that occurred approximately 20 miles north of the most recent incident. The NTSB’s investigation is expected to take several months.

The Federal Railroad Administration also has directed Amtrak to perform an immediate review of its basic work-safety protocols and focus on rectifying alleged deficiencies in communication between maintenance crews and dispatchers.