Crash-test ratings vary around the world. Driven assesses the safety raters for their depth of information.

Safety sells these days and so often, crash-test results are the currency. Star ratings are everything: five is a seal of approval. Anything less seemingly puts the safety of a new car into question.

So much depends on those stars. But what do they really tell us? A lot in a comparative sense. Worryingly little in many real-world situations.

Those stars could come from any number of crash-test programmes. The most relevant for New Zealand consumers is the Australian New Car Assessment Programme (ANCAP), because the models tested are generally the same as those sold here. The NZ Transport Agency and NZ Automobile Association are both members of ANCAP.

ANCAP's star ratings are based on four basic laboratory crash tests, which are identical to those used in the parent EuroNCAP. There's a frontal offset crash, in which 40 per cent of the driver's side of the car is crashed into a metal barrier at 64km/h. In the side impact test, a 950kg trolley is propelled into the car at 50km/h. The pole test takes place at 29km/h, with the vehicle sliding sideways into a rigid object. Cars are also tested for pedestrian impact at 40km/h. In all cases, crash-test dummies take all the abuse on behalf of us consumers.


While carmakers tend to market these results in terms of simple star ratings, the results of each crash test are painstakingly documented by ANCAP and available on its website: Points are awarded for individual impacts, with bonuses awarded for extra safety features like stability control and seatbelt reminders.

While Ancap is based on EuroNCAP, it's important not to confuse the two. EuroNCAP's testing regime is slightly different, also including child protection (introduced in 2003), whiplash (2009) and a completely new rating system introduced in 2009 that incorporates all of the above plus bonuses for innovative safety systems introduced by carmakers.

These days, anything less than a five-star rating is considered a failure. It wasn't always so. NCAP was formed in 1997, and when the Volvo S40 achieved four stars that year it was considered exceptional. The Renault Laguna was the first to be awarded five stars, in 2001 - a feat regarded as impossible up to that point.

The first rule is that you can't compare test results from different crash-test programmes. The second, more sobering one is that you can't even compare results from the same programme for cars of different sizes. Lab testing of the ANCAP kind gives valuable data on how cars of similar kerb weight compare in collisions with solid objects or each other.

In the real world, cars of different sizes and heights also crash into each other. Unpalatable as it may be, weight overrules even the most impressive star ratings. ANCAP argues that there is plenty of evidence to show vehicles performing well in its crash tests are also safer than average in real-life crashes. That makes sense. The more stars, the safer the car.

But it's an inescapable fact that if a 2.5-tonne SUV crashes into a 1500kg hatchback, it's not star ratings that will determine the outcome: it's the laws of physics. You'll be better off in a five-star hatchback than in a two-star one. But probably not better off than the occupants of the SUV.

Arguably, there's too much consumer focus on laboratory crash testing, although programmes like EuroNCAP have forced the industry to prioritise new safety technology.

The Used Car Safety Rating programme has run for two decades and takes a different tack on crash safety. Its results are based on studies of how particular vehicles perform in real-world crashes on Australasian roads, with data collected and analysed by the Monash University Accident Research Centre. For 2012's Used Car Safety Ratings, over four million crashes were analysed. Vehicles are awarded star ratings (unrelated to ANCAP ratings) and those considered to give occupants and other road users the best possible protection are given a "safe pick" stamp. The 2012 Ratings cover models from 1996 to 2010. The star ratings are applicable and comparable for vehicles of different sizes and weights, although the 2012 results cannot be compared with earlier editions.

The results of the 2012 Used Car Safety Rating programme are on the NZ Automobile Association website.