In an Australian first, car doors developed for passengers' comfort with bumps, curves and arm rests that stick out, have been found to increase the risk of injuries and deaths of children in a crash.
The position of arm rests can increase the likelihood of a child having a head injury in a crash by as much as 52 per cent, according to researchers from the Transurban Road Safety Centre at Neuroscience Research Australia (NeuRA).
Intrusions from objects in a crash have been identified as the primary cause of death in 58 per cent of cases.
The results were discovered during a dozen crash tests using new equipment developed by engineering undergraduates to test different shaped car doors in a side impact crash.
The results were unexpected, said Associate Professor Julie Brown, co-director of the Transurban lab which conducted the tests.
It also explains findings by the Ombudsman this year which found "significant intrusion" or "intrusion affecting the space occupied by the child" was a factor in almost three-quarters of the deaths of 66 children, aged zero to 12 years, who died in NSW.
Associate Professor Brown said it was the first time Australian researchers had been able to examine how child restraints function when there is an intrusion of the back car doors from a side impact.
Most crash tests for side impact crashes worked on the assumption that side doors were flat as they were when they were first introduced, said Dr Brown.
But over the years car doors have changed shape and now include arm rests that may protrude into a child's car restraint.
“We have the opportunity to increase safety in cars by improving the shape of the armrest and door. This would make it less likely that a side-on collision will result in death or serious injury of a child,” said Associate Professor Brown.
The researchers found that the position of the arm rest alters the movement of booster seats and this can influence head injury risk.
A mid-height armrest was found to be most problematic compared to both low and high arm rests.
A completely flat door was safer than all arm rests.
Dr Brown said the findings opened an important new field of research: “This is an important development because side impact crashes are responsible for most of the serious head injury that occurs to correctly-restrained children,” she said.
“There is a huge range of arm rests and rear door shapes in current vehicles. Our work shows the need to find the best design to minimise injury risks caused by the door shape or position of arm rests.”
The Ombudsman report found the most common source of fatal injury in children who correctly used age appropriate restraint systems was intrusion into the child’s occupant space.
It found the crashes in which the children died were "generally high energy crashes" (that is, high speed crashes).
That results in the car door being pushed into the children's space. Anything that intrudes (from a protrusion like an arm rest) is more likely to cause death or injury at a high speed.