Train driver Shaun Burton, 60, died and about 100 people were injured when one London-bound service crashed into the back of another on Friday.
The Rail Accident Investigation Branch (RAIB) said in an interim report that Burton's train proceeded past a red signal near the scene of the crash in Elstow, near Bedford at 17:15 BST on Friday.
It added that "it is not yet possible to say what indication the driver received" from automatic warning system (AWS) equipment fitted to the train.
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