Passengers on a London to Southend service discovered a train door was left open for 23 minutes - while the train was moving at 80mph.
One passenger reported the open door to the driver at Hockley station, in Essex, at 07:20am on 22 August.
Safety digest to be prepared following a passenger train door open in traffic incident, Essex, 22 August 2019. https://t.co/qHqW7Q5CmI— RAIB (@raibgovuk) September 5, 2019
The Rail Accident Investigation Branch (RAIB) said the train traveled for 16 miles with a passenger doorway wide open.
The RAIB has conducted an investigation and is due to release a "safety digest" at a later date.
A spokesman said: "We have undertaken a preliminary examination into the circumstances surrounding this incident.
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“Having assessed the evidence which has been gathered to date, we have decided to publish a safety digest.
"The safety digest will be made available on our website in the next few weeks."
Martin Moran, Greater Anglia commercial and customer service director, said: “Safety is our highest priority.
"We immediately took the train out of service when this happened and carried out our own investigation into the incident.
"We have also carried out checks on every single door on that type of train that we have.
“No-one was injured in this incident and there have been no further incidents since.”
In July, a report by the RAIB found that a Tube driver’s lack of sleep and food may have contributed to 10 doorways being open as a Jubilee line train travelled between two stations.