Original sentence: And within days of the derailment, Amtrak had completed that ATC installation on the northbound track, apparently with none of the regulatory-requirement delays attributed to PTC.But officials later admitted that the incident could also have been prevented by the activation of an existing simpler and cheaper system, ATC (Automatic Train Control), which had been operational for years on the southbound track of the curve at which the derailment occurred, but not on the northbound track.Officials at first said that the incident might have been prevented by PTC (Positive Train Control), a computerized speed-limiting system that was operational elsewhere on the Northeast Corridor, but whose activation at the crash site had been delayed due to regulatory requirements
Edited sentence: Officials said that the incident might have been prevented by a computerized speed-limiting system that was operational elsewhere on the Northeast Corridor, but whose activation at the crash site had been delayed due to regulatory requirements