Shaun Burton, 60, died when the East Midlands Railway (EMR) train he was driving hit the back of a stationary train run by the same operator.
The Rail Accident Investigation Branch 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 5.15pm on Friday.
It added it is not yet possible to say what alert the driver received from an onboard system designed to sound a horn when a red light is being approached, and activate the emergency brake if that is not acknowledged by them pressing a button.
About 160 people were injured, 102 of whom needed hospital treatment.
Fifty-three remain in hospital, including eight in a critical condition.
Images from a forward-facing CCTV camera on Burton's train show a signal near the scene of the crash "was displaying a red aspect as the train approached and then passed it," the interim report said.
Preliminary analysis of a data recorder recovered from the wreckage shows it was travelling at 122km/h when its brakes were applied nine seconds before the crash.
Its speed had reduced to 79km/h when the impact happened.
Burton's train was fitted with automatic warning system equipment triggered by magnets on tracks.
This sounds a bell or chime in the driver's cab when it is approaching a green signal, and a horn when coming up to a non-green signal.
In the case of the latter, drivers are required to acknowledge the warning by pressing a button.
After this happens, a visual indicator appears in the driver's cab as a reminder.
The train's emergency brake is applied if the warning is not responded to quickly enough.
The RAIB statement said the stationary train involved in the collision had come to a stop "unexpectedly" after a fault with its AWS equipment caused its brakes to apply.
This resulted in the signal behind it automatically changing to red, investigators said.
Approaching trains should stop at red signals.
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