It was caused Causation when a busy signalman , Alfred Sutton , forgot GiveUp about a pair of light engines waiting Motion at his down ( northbound ) starting Process_start signal to return Arriving to their shed at Carlisle .

At the time of the accident Catastrophe , both passing loops were occupied Control with goods trains and a northbound local passenger train was standing Placing on the southbound main line .

A minute later the wreckage was struck Attack by a northbound sleeping car express train travelling from London Euston to Glasgow Central .

With the northbound loop occupied Control , the northbound local train had been reversed Change onto the southbound line to allow Preventing_or_letting passage of two late running northbound sleepers .

With the northbound loop occupied Control , the northbound local train had been reversed Change onto the southbound line to allow Preventing_or_letting passage of two late running northbound sleepers .

With the northbound loop occupied Control , the northbound local train had been reversed Change onto the southbound line to allow Preventing_or_letting passage of two late running northbound sleepers .

Shortly after the derailment Catastrophe , Amtrak completed Process_end ATC installation Building on the northbound track .