A schoolgirl who had trouble sleeping died when she fell onto a moving train after she went out for a run to burn off energy.
Zoe Miller, 13, fell from the parapet of a bridge over the West Coast main line after becoming disorientated, an inquest heard.
She often went out late at night to 'skip and run'.
Det Insp Andy Rose of British Transport Police said: "Zoe was not a good sleeper and it was not unusual for her to go out late at night and run around.
"She had a considerable amount of energy and it was not uncommon for her to skip, run and burn off energy."
The inquest heard she had been standing on the parapet of the bridge when a southbound train heading for Euston passed underneath at 60mph.
In darkness, and disorientated by the noise and rush of air, she lost her balance and fell on to the train. Her body was found on the tracks the next day.
The inquest heard the lively teenager experienced difficulties going to sleep at night.
When that happened her parents, Bob and Jane Miller, had become used to her going out in the back garden at their home in Berkhamstead, or further afield.
Graham Danbury, deputy coroner for Hertfordshire, recorded a verdict of accidental death.