Car size matters in safety, say experts
Philip King, Motoring editor From: The Australian February 23, 2010 12:00AM

A SMALL car would always come off second best in a collision with a heavier vehicle and it was more difficult to make them safe, experts agreed yesterday.

Just nine models on sale in NSW fall below the 975kg threshold for the transport levy and, with the exception of three Lotus sportscars, all are lightweight runabouts with a range of crash test results.

Two -- the Fiat 500 and Mazda 2 -- achieve the maximum five-star crash rating commonplace for larger vehicles.

Jack Haley, a technical specialist with the NRMA, which sponsors the New Car Assessment Program crash tests, said many drivers were more comfortable with small cars and manufacturers were now fitting sophisticated safety features, such as multiple airbags and electronic stability control.

Mr Haley said the aim of crash-test ratings was to help buyers make informed decisions.


"People normally buy a vehicle within a certain size range, and we try to steer them towards the safer vehicles in that range," he said.

He said smaller vehicles could be engineered to absorb crash energy effectively, but there was no dodging physics.

In multiple-vehicle collisions, weight played a role and occupants in a heavier car would be better off. "Mass has an effect," he said. "A car that's twice as heavy has twice the energy."

Stuart Newstead of the Monash University Accident Research Centre said that driving a car weighing less than a tonne -- much less than the fleet average of 1450kg -- meant you were automatically at a disadvantage.

"If you're in something light you're going to get hit by heavier things on average," he said.

Smaller cars were also more dangerous in single-vehicle crashes. "They have less room to absorb impact energy and inside the vehicle there's less survival space," he said.

Crash results gave a distorted picture, Dr Newstead said, because not all stars were equal.

"It's much harder to design a small vehicle that is ultra-safe," he said. "The NCAP ratings don't reflect that because their tests are independent of mass."

He said that as people were encouraged into smaller vehicles for environmental reasons, it was important to recognise that there was a safety trade-off.