A rail worker was killed after failing to move off a track as a train approached, a report said.
The train from Northampton to London Euston struck the worker near Roade, in Northamptonshire, on 8 April 2020.
The report said the worker was "not averse" to walking across open tracks.
It found engineering firm AmcoGiffen did not have "adequate arrangements to encourage compliance with safety rules" at the site. The company said an investigation was ongoing.
An AmcoGiffen spokesman said its thoughts remained with the family, friends and colleagues of the employee "who lost his life in the conduct of delivering essential rail services".
"Given this incident remains the subject of ongoing investigations, we are unable to comment further at this time," he said.
The Rail Accident Investigation Branch (RAIB) report said the driver of the London Northwestern Railway train saw the 51-year-old man on the track, sounded the train horn and applied the emergency brakes.
The train, which was travelling on the West Coast Main Line at about 90mph (145 km/h), hit the man, who was part of a group undertaking civil engineering work.
Its report said the man, who was in charge of the project and controller of site safety, had been "walking along a line that was open to traffic".
He acknowledged the train's warning horn by raising his arm but "did not look towards" the train.
Investigators said it was not certain why he had gone back on to the track after agreeing with the signaller that the line would reopen after a closure to undertake isolation of overhead lines.
Evidence also suggested he "did not always work in a way that was consistent with rules, standards and procedures".
Colleagues had previously challenged him for not looking towards trains when acknowledging them and said he was "not averse to walking along the railway when it was open to traffic, without any formal protection".
The report said his "occasional non-compliant behaviour had not been identified and addressed" by his employer.
It added it was possible that the deviation from procedures was "driven by his enthusiasm to maintain progress" on site.
The RAIB said it had made recommendations to AmcoGiffen after finding it did not have formal performance monitoring and appraisal arrangements to identify development needs and that its site did not have "adequate arrangements to encourage compliance with safety rules".