Collision course

Proposed European crash tests could mean that cars need to be redesigned to make them safer. Paul Carslake reports

Strip out all the safety equipment in a modern car, and you could reduce the cost by 20%,’ reckons Graham Townsend, director of engineering at the Motor Industry Research Association.

Put another way, safety equipment and engineering amounts to a sizeable part of the component and development costs of a vehicle. It is a big business, and a lucrative one, especially for Mira’s vehicle safety testing laboratories, and it is growing fast.

The driving force is legislation from the European Union, which is responding to growing demands from an increasingly clued-up car-buying public. The big safety milestone car makers have been working to is a pair of EC directives that come into force in October 1998, laying down new crash test procedures for frontal and side impacts.

Current standards, dating from 1974, bear little resemblance to real life accidents, with the car being crashed head on into a concrete block. The pass/fail criteria are simply based on how much the steering wheel is shoved back into the cabin.

The new tests are more sophisticated, and replicate a badly judged overtaking manoeuvre that goes wrong: the driver’s side only of the car is crashed into a deformable barrier made of aluminium honeycomb structure that crumples on impact just as a car would do.

In addition, there is a side impact crash test. And for the first time ever, injury criteria measured by crash test dummies must meet strict standards if the vehicle is to pass the test.

Car makers, though, are several steps ahead. They are already designing cars that meet more sophisticated tests than these legal minimum requirements, in anticipation of a tightening up of EU crash requirements, and to meet even stricter laws coming up in the US. These could even include new measures – currently up for discussion in a draft European Commission directive – to make cars safer if they hit pedestrians.

If such legislation is adopted, this would result in radical changes to the shape and size of current cars.

The front end would be flatter, as protruding front bumpers cause too much damage to the lower legs of pedestrians. Radiator grilles – which have made a comeback in the past five years – may have to go, as car makers start to model cars which absorb more energy. But most noticeable of all would be an increase in the bonnet height.

In the typical road accident when a car hits a pedestrian, the body makes impact with the car in a strict sequence. First the bumper rams in below the knees. Then the grille hits the upper leg, and the torso slams down on to the bonnet, with the head making impact last of all, determining more than anything else the severity of the injuries.

What is underneath the bonnet where the head hits is critical. The point at which the head hits the bonnet depends on the height of the victim and the length of the bonnet, and is referred to as the wraparound height – because of the unpleasant way in which the lower part of the body gets caught under the front of a car during impact.

If the proposed legislation goes ahead, car makers will have to create more space between the car bonnet and the top of the engine or any other hard points, like washer bottles or the battery. The nearer the impact is to the windscreen, the more space will be needed under the bonnet, because it is this zone that the tallest adults (with heavier heads and more momentum) hit the car with the greatest energy. At this point, about 80mm of deformation space is required. Nearer the front of the car, about 50mm of space will be needed. Typical cars today have gaps of as little as 20mm in places.

‘If the new legislation is introduced, then there is no doubt that within a few years we will see a distinct change in the way that cars are designed,’ says Gary Brown, a Mira project engineer working on pedestrian impact.

Brown’s work is carried out not with complete anthropomorphic models (dummies) but by using simulated parts of the human body fitted with deceleration sensors, fired into the car by air pressure, with the pressure variable to create different and precise impact speeds.

But designing cars with a soft outer skin will cause other problems. In the US, cars must withstand low-speed impacts such as a parking shunt with minimum deformation of the bumper. This is completely at odds with the principle of engineering cars with more ‘give’ in the bodywork to absorb the force of pedestrian impacts. The resulting vehicles would bend more easily and cost more to repair – with insurance policies rising as a result.

Meanwhile though, car designers must contend with a more immediate design challenge, set by the new European National Car Assessment Programme (Euro NCAP).

This is a series of frontal, side impact and pedestrian crash tests designed to test cars beyond current legislative requirements and provide consumer information on the results. It is led by a consortium which includes the Department of Transport, European consumer watchdog bodies, the RAC and AA, and the Transport Research Laboratory, the former Government agency which is now privatised – and still independent – and which is carrying out the crash test programme.

Car makers have given Euro NCAP a cool reception. The NCAP test is carried out at 64km/h instead of the 56km/h of the standard European Frontal Crash Test, and ranks the set of rival cars tested in any one size group from best to worst.

The results have proved controversial. Some cars designed to meet the current legal safety requirements performed particularly badly in the NCAP tests.

Mira has carried out NCAP standard tests confidentially for car makers anxious to see how their vehicles will fare. But Townsend is keen to distance himself from the programme, describing it as a distraction for car makers already occupied with testing for EU regulations. ‘We’re not entirely happy with what NCAP is doing at the moment,’ he says.

Specifically, Mira engineers have two main criticisms of the Euro NCAP test. One is that with vehicles of a higher mass travelling at this speed, the deformable barrier (designed for the 56km/h crash test) is fully crushed and the car rebounds off the back wall – a process known as bottoming out. That can lead to complications in assessing the data, engineers claim.

The TRL denies this. ‘Most car manufacturers would prefer that this kind of consumer information would just go away,’ says Adrian Hobbs, head of crashworthiness at TRL, a recognised authority on impact testing techniques. ‘Mira is funded by car makers and component makers, and it is simply restating the industry’s position.’

Hobbs says the bottoming out effect is not a major problem, as the most important impact characteristics occur before then, and bottoming out happens in real life accidents too. ‘It’s not perfect. But we know of no solutions now that would make this crash test better given our current technology,’ he says.

Mira engineers also claim that judgements of the crash effects go beyond simple structural intrusion or deceleration measures on the dummies, to a point that Mira engineers think is too subjective.

Not so, says Hobbs. In the standard crash test, for example, the dummies’ knees are always in exactly the same position. The result, according to Hobbs, is that car makers position hard components behind the facia knowing that the dummy’s knees will not make contact on impact, even if they do smash through plastic coverings on the dashboard.

In reality, drivers’ leg positions are more varied. It is this kind of nuance that the NCAP test is including, and marking down cars in the overall assessment if they are found to have components within a measured risk zone that could cause injury.

‘The Volvo S40 and the Vauxhall Vectra did well in the NCAP tests simply because they thought about this kind of real life risk in the design of their cars,’ Hobbs says.

While the NCAP test is controversial, its basic format is similar to the standard EU test. The deformable barrier creates the kind of impact a car would undergo if it crashed into a mirror image of itself – a car of equal mass and structural rigidity.

But there is debate within the industry about an even more sophisticated crash test regime which could be even more problematic.

Ingo Kallina, Mercedes’ head of vehicle safety, thinks the next step facing car makers is to give drivers of small cars a better chance if they crash into heavier vehicles.

Mercedes’ interest in such technology is clear: it wants to create an environment where drivers of its new small cars like A-Class or the MCC Smart Car, will fare better in a smash with an E-Class or S-Class, so that it can promise security to all its customers.

To do this, Kallina thinks heavier cars should be tested at a lower speed than smaller cars, allowing them to have a softer structure that will deform more quickly on impact with a small car, which by contrast would have a harder and more rigid bodyshell.

‘You can’t cheat the laws of physics, but by allowing the vehicle with the greater mass to absorb more energy, the smaller vehicle will stand a better chance,’ Kallina says.

Hobbs says the TRL has also been looking at this issue of compatibility between small and large cars, but is unconvinced by Kallina’s line. ‘I don’t agree with Ingo on this, because in the end drivers of bigger cars will not be protected if they crash into a similar, or heavier car, or a wall for that matter,’ he says. ‘And what is to stop manufacturers of small cars increasing the mass just to get the car through the easier low-speed crash test? It wouldn’t work.’

The compatibility issue demonstrates the limitation of where passive crash safety engineering can go with current materials and technology. Many engineers now believe the next frontier of vehicle safety can only come from intelligent systems that actively avoid vehicle impact accidents happening in the first place, rather than simply try to control the consequences.