CAR bonnets that pop up slightly if the car hits a pedestrian could
dramatically reduce deaths and head injuries. Raised quickly enough, the hood
would deform and cushion the blow, stopping the accident victim from striking
the solid parts of the car underneath.
Autoliv, a Stockholm-based transport safety research and development company,
has put together a prototype system that does just that. Steel bellows under the
bonnet fill with gas in less than 70 milliseconds and lift the rear edge by 10
centimetres. In a typical collision at 40 kilometres per hour, the victim鈥檚 head
hits the bonnet about 150 milliseconds after the bumper first hits their legs,
says Yngve H氓land, research director at Autoliv. The company revealed its new
system to the Enhanced Safety of Vehicles conference in Amsterdam earlier this
month.
The rear-opening bonnet鈥檚 superfast reaction is triggered by accelerometers,
which are installed in the front bumper. 鈥淭hey analyse the speed of bumper
deformation to tell the difference between a human leg and a signpost,鈥� says
H氓land. His team is already working with car manufacturers to develop the
technology and they hope to see cars fitted with a system roll off the
production lines in under four years. It will probably be used alongside
external air bags to cushion pedestrians from the windscreen and front
pillars.
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Graham Lawrence, a research scientist at the Transport Research Laboratory in
Crowthorne, Berkshire, says: 鈥淭he lifting bonnet looks very effective, and it
wouldn鈥檛 be the end of the world if it false-triggered.鈥� A spring-powered
bonnet-popper developed by the laboratory in 1985 failed because its triggering
system was not powerful enough.
Autoliv says its invention performed impressively in the key safety test used
to assess the risk of life-threatening injuries to the brain, known as the Head
Injury Criterion (HIC). This is an index calculated by measuring the forces on
dummy head in an impact. The proposed European limit
(see Graphic) of 1000 HIC
represents a 15 to 20 per cent risk of serious brain injury for an adult. Impact
points for the test include unyielding parts of the bonnet such as those above
the camshaft cover, and over the suspension struts to the right and left.
In Europe alone, about 7000 pedestrians are killed each year when struck by
cars. Within the next month, the European Commission is expected to announce
that car makers must rethink their vehicle designs to reduce the death toll.