Motorist Leigh Smy probably fell asleep behind the wheel of his car after drinking at a nightclub, an inquest heard.
Mr Smy, 22, of Rose Hill, Oxford, died when a friend's car he was driving careered off the A420 near Swindon and smashed into a wall at 75mph.
The inquest at Swindon police station heard how the car was almost split in two by the force of the crash which threw Mr Smy 30 yards into the River Cole.
In a statement made to the court, police vehicle examiner Stephen Dudley said the wreckage was barely recognisable as a car.
Police accident investigator Pc Matthew Stone told the hearing that the car Mr Smy was driving, a Maestro, suffered massive structural damage in the crash. The force of the impact had spun the car around.
Pc Stone said by examining the scene it was possible to tell that Mr Smy had not tried to swerve or put his brakes on but had left the road and the car had not stopped until it had hit the wall and come to rest on a river bank.
He said one possibility was that he had fallen asleep at the wheel.
The crash happened on December 10 last year after Mr Smy had spent the evening with friends at the Brunel Rooms nightclub in Swindon.
The inquest heard how, when they arrived at the nightclub, Mr Smy said he would look after the keys to the Maestro which belonged to one of the friends.
During the evening, Mr Smy was thrown out of the club by a bouncer, although none of his friends could say why. By the time they had gone out to meet him by the car, he and the Maestro had gone.
Although a post-mortem examination revealed Mr Smy was slightly over the drink drive limit, his friends said he did not have much to drink and was having a good time at the club.
Wiltshire deputy coroner William Baiche returned a verdict of accidental death.
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