The car a Buckinghamshire driver died in during a crash did not give the protection expected, an inquest heard.
Judith Evans, 56, from Aylesbury, was driving a Peugeot 107 on 20 January 2009 when she was killed in a head-on crash with a Vauxhall Vectra.
Coroner Richard Hulett said the car's safety equipment was not faulty but did not save her life.
He recorded a verdict of death by misadventure at High Wycombe Magistrates' Court.
Mrs Evans suffered multiple fractures, chest injuries and abdominal injuries in the crash.
"In the event, Mrs Evans did not enjoy the benefit of the combined restraint package which was designed to work together," Mr Hulett said.
"The seatbelt had extended to its furthest extent, the airbag didn't give her the protection we would hope and the anti-submarining ramp didn't stop her from submarining.
"This doesn't mean the equipment was faulty but at the end of the day it didn't save her life."
The hearing was told that Peugeot had not crash-tested the car with a dummy for any driver weighing more than 12 stone 4lb (78kg).
Mrs Evans weighed almost 16 stone (101.6kg).
Peugeot safety expert Richard Zeitouni told the inquest: "When we designed this car we found it was good, adequate protection for the majority of occupants.
"It's an official dummy, a regulation dummy."
Peter Gloyns, a mechanical engineer at Vehicle Safety Consultancy, said the car's restraint system did not appear to have worked in the way it would be expected to.
"The accident raises a serious question over the stability of the response of the total restraint system for an occupant of this build and weight in an accident of this severity in which it would be hoped that good protection could be offered," he said.
The inquest also heard that Mrs Evans, normally a cautious driver, was travelling on the wrong side of the road and may have suffered a medical condition before the collision.