A charity worker who was nearly twice the drink-drive limit died of a head injury after leaning out of a train window at 75mph.
Bethan Roper, 28, hit a tree branch on the Great Western Railway service near Bath after a Christmas shopping trip with friends on December 1.
Network Rail had not carried out a tree inspection at the scene since 2009, a report by the Rail Accident Investigation Branch (RAIB) revealed on Wednesday.
It also said a notice on the train door had failed to convey how dangerous it was to lean out of the window.
Miss Roper, of Penarth, near Cardiff, had been to the Christmas markets in Bath. After boarding the London Paddington to Exeter train, she and her friends stayed near the doors because the carriage was full. At least one of her companions leaned out of the window before she did, the report said.
Miss Roper hit the tree branch at 10.04pm and was pronounced dead at Bristol Temple Meads station a few minutes later.
A toxicology report found she had 142mg of alcohol per 100ml of blood – the legal drink-drive limit is 80mg. The train door was fitted with an opening ‘droplight’ window to enable passengers to use the handle on the outside when they needed to leave the carriage.
The report found a warning sign that used the word ‘caution’ above the window met industry guidance but ‘did not adequately convey the level of risk’.
Investigators also noted that it is much smaller than other signs around it and its background colour was yellow, when red would have been more appropriate to convey danger.
The report said: ‘Witness evidence indicates that the passenger had her head out of the window for a few seconds before falling back into the vestibule having sustained a serious head injury.’
After a passenger died leaning out of a window on a train in south London in August 2016, Great Western Railway completed a risk assessment of its droplight windows.
This resulted in a plan to install enhanced warning signs with a red background by May 2018, but this had not happened by the time Miss Roper was killed seven months later. The signs were updated after her death.
Miss Roper worked for the Welsh Refugee Council charity and was chairman of Young Socialists Cardiff.
Her father Adrian said in a statement after her death that his daughter ‘enjoyed life to the full whilst working tirelessly for a better world’.