A rail worker who was struck by a train during a track patrol had received “ineffective” safety briefings beforehand, an investigation found.
The woman was acting as a lookout on the tracks close to Chalfont and Latimer station in Buckinghamshire in April 2022.
She was treated in hospital for head and body injuries she sustained.
A spokeswoman for Transport for London (TfL) said safety was its “top priority”.
The report, by the Rail Accident Investigation Branch (RAIB) said the train was travelling at approximately 25mph (40 km/h) at the time of the incident.
Chalfont and Latimer lies on the Metropolitan Line of the London Underground, part of Transport for London.
The woman, who was working for an agency, was released from hospital the same day but had “continued to suffer from the effects of the accident”, the report said.
It said she was “not familiar” with the location and “safety briefings provided to her on the day were not effective at giving her the information she needed to work safely”.
Investigators said there were “underlying factors” including London Underground’s processes for managing track safety “not adequately controlling the risk to staff working on the line in traffic hours”.
The RAIB made four recommendations to London Underground Ltd, part of Transport for London (TfL) , including reviewing the need for track work while trains were running – and improvements to safety processes and reporting.
Andrew Hall, the RAIB chief inspector of rail accidents, said: “Track worker safety continues to be an ongoing theme for the Branch.
“This accident is an alarming reminder that there is still work to be done to reduce the likelihood of track workers coming into contact with trains on parts of the railway.”
He highlighted a need for the “importance of good planning, clear safety procedures, effective leadership, site discipline and fulsome briefing”.
Lilli Matson, TfL chief safety health and environment officer, said safety was the company’s “top priority” and that the firm had been “extremely concerned” by the accident.
She said: ” We will now consider the findings of the RAIB’s report and have already put a number of actions in place to ensure this type of incident does not occur again.”