A railway worker who was killed by a train was tired and probably worrying about having to cover for his brother, a report has found.
The man died when he was hit from behind at 69mph (111km/h) in Croydon, after midnight on 6 November last year.
Investigators found the man, who was on a zero-hour contract, had moved away from the section of track which had been protected for workers.
Network Rail said it was "reviewing our standards and our supplier practices".
The worker had put warnings on the tracks to allow others to remove litter, but then walked along sleepers in the middle of the rails to Stoats Nest Junction, Purley.
A Southern train approached from behind and in spite of the driver repeatedly sounding his horn and applying the emergency brakes, he was run down.
Inspectors from the Rail Accident Investigation Branch (RAIB) discovered the man was meant to be assisted by his brother that night.
However, earlier that day his brother had called to say he was too tired to attend as he had been working as a delivery driver and asked him to forge a signature to say he was there.
Investigators found as well as worrying about what would happen if he was caught, he had also only had 3.5 hours sleep as he had been helping to decorate a friend's house.
The RAIB found the use of staff on zero-hour contracts created conditions "in which it is difficult to manage fatigue effectively"
It recommended both Network Rail and Vital Human Resources, who employed the railway workers, should review their practices.
Sam Chessex, Network Rail acting route managing director, said the firm "does not use zero-hour contracts, and our code of conduct sets out what we expect from suppliers who do use them to ensure contractor safety".
A spokesperson for Vital Human Resources said: "The health and safety of our workforce is our main priority and a core value within our business."