Katie Dagley, 19, was driving home from work when she approached a single lane bridge controlled by lights that had malfunctioned just 20 minutes earlier.
She drove her Ford Ka onto the bridge and collided with an oncoming Fiat Punto.
The teenager, who had dreamed of becoming a chef, was pronounced dead at the scene.
Senior police investigator Andy Stevens told an inquest into her death that he had carried out a detailed examination of the scene in Alvecote, near Tamworth, West Mids, and confirmed that the traffic light fault was caused by a trail left by a slug or a snail.
He said: "There are traffic lights at either end and there are white lines across the road.
"The fault was logged at the monitoring agency and sent to county highways at 10.52pm, some 20 minutes before the collision.
"The reason for the fault was due to a slug or a snail.
"There was a trail across the circuit board and it had short-circuited it – it was one of those things, it's a tragedy."
Warwickshire Coroner Sean McGovern returned a verdict of accidental death at the inquest in Coventry last week.
via Teenager killed after a slug causes traffic light failure - Telegraph.