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Crash course

Highways Road safety

Thirty five vehicles were trashed during trials for a new safety barrier system. But it could have been a lot more, reports Dave Parker

In 1988 the UK Highways Agency commissioned a barrier impact test at the Motor Industry Research Association's (MIRA) test facility. A 1.5t executive saloon - a Rover SD1 - travelling at around 110km/h slammed into a standard open box beam (OBB) steel barrier at 20°.

The barrier deflected no more than 800mm, the Rover suffered substantial damage, but readings from the instrumented crash dummy in the car indicated the occupants would have survived relatively unscathed.

Ten years later the Agency repeated the test, this time using a Ford Mondeo family saloon - which also weighed in close to 1.5t. Again, the results showed that any occupants of the Mondeo would have escaped with only a severe shaking. This time, however, the barrier came off worse, deflecting 1.3m.

Damage to the Mondeo itself was much less than to the Rover a decade earlier.

New European standards for safety barriers were the motivation for the repeat test. Corus Automotive safety engineering manager Martin Batchelor says that the new standards 'reflected the big changes in car design over the last few years'.

He explains: 'Each class of car has got bigger and heavier.

At the same time the car manufacturers have invested heavily in advanced computer aided design techniques to meet increasingly tough requirements on occupant safety. The result is that modern cars behave very differently in crash situations to those designed decades ago.' In practical terms the main result of the second Agency test was a reclassification of that particular type of barrier. One of the key parameters of safety barrier classification is the 'working width', effectively the distance the barrier will deflect under the standard impact. The higher the working width, the greater the stand-off distance between the barrier and any solid object - or contra flow traffic - behind it. Thus when space is tight a stronger more expensive barrier is needed.

For decades most barriers installed on the UK roads network came from a range of standard designs originally developed by the Department of Transport in the 1970s. Over the years the designs evolved, and more variations and components were introduced to meet all possible combinations of location and protection. By the turn of the century the available systems had become complex, expensive, and hard to maintain.

The gency sponded to the new standards by effectively abandoning its largely prescriptive approach to barrier specification. Manufacturers would be allowed to develop their own designs - in any material - and these would be approved provided they met the new performance requirements.

But acceptance would depend on crash testing - an expensive exercise. Developing a wide range of new products was potentially a very costly process.

'Customer feedback indicated that what the market wanted was a simple, low maintenance system which would integrate if necessary with both tensioned corrugated beam and OBB systems, but which offered higher performance, ' reports Corus Distribution & Building Systems account manager Jo Larkin. 'This meant an untensioned system, using familiar components wherever possible.' In early 2005 the Agency went for the high containment HGV-proof concrete barrier for central reservations on heavily trafficked roads. But concrete would only replace steel when major upgrades took place - smaller projects would still be open to alternatives. Corus would be competing for the rest of the market with tensioned rope systems - in the short term at least.

Responsibility for developing the new product - eventually to be dubbed Vetex - fell to the Corus Automotive team based at the University of Warwick.

Normally the 30 engineers and materials specialists concentrate on developing better, more ef'cient steel components and body shells for car producers.

Safety barriers were a new challenge, but the team was well equipped to face it.

'We've got some very advanced computing facilities here, ' Batchelor says. 'A finite element model of a car will have around 400,000 elements; a simulation of a collision will generate 3GB of data and take up to 36 hours to run.' Barrier models were of much the same scale as the car models. 'Luckily we were able to use a model of MG Rover's 75 saloon [as the vehicle in the virtual crash test], which saved us a lot of time, ' explains Batchelor. Data was processed by Dyna 3-D dynamic 'nite element analysis software.

To check its initial assumptions the team ran a simulation of a Rover 75 hitting one of the standard barriers - then carried out the real life equivalent at MIRA and compared the video with the simulation.

'Agreement was very good, at more than 95%, ' Batchelor reports. 'In the simulation you can see a bolt head from the barrier spinning away - and in the video the same bolt head is visible taking almost exactly the same path.' With their model validated the Corus team was able to get down to new product development. Progress was rapid. Different barrier designs could be put through simulated collisions with different vehicles: the designers could try out variations in post size and spacing and materials thickness, and there would be no need for real life testing until a satisfactory design was finalised.

Actual real life testing was minimised. Accreditation testing could be approached with real confidence. 'We had a success rate in excess of 85%, ' says Batchelor. 'This compares to the normal success rate of closer to 50%.' All results from full scale testing were used to refine the finite element models. Naturally Corus concentrated on getting the most popular category onto the market first. In November last year it launched the Vetex normal containment range, which, with post spacings ranging from 0.8m to 5m, offered a wide range of working width performance.

With it came a simple, quick to install end terminal. Overall, the number of components in the system was 90% fewer than the standard product, a popular feature among potential customers.

The next step was a big one by normal standards. Corus developed a twin rail high containment version of Vetex, which meant passing a test where the test vehicle was a 13t single deck bus.

'This would have been a very expensive exercise without our simulation technology, ' Batchelor points out. 'In the event the first full scale test went very well, and the bus sustained so little damage we were able to patch it up and use it again for the accreditation test.' In fact Corus had more trouble with the standard test involving a 900kg small car, he adds. 'There aren't many cars that light anymore. In the end we had to develop a model for the Suzuki Swift based on work done at George Washington University in the US.' Simulations predicted - and full scale testing con'rmed - that the little Suzuki would sustain major damage in the standard 110km/h impact.

But instrumentation again revealed that the occupants would survive without serious injury.

So far 35 vehicles have made the ultimate sacrifice - but Corus now has Agency approval for a wide range of Vetex options. Batchelor says that without the simulation technology many more would now be in the scrap yard. Later this year a three rail bridge parapet version will be launched and other high containment options are in the pipeline.

'We're also discussing our high containment option for central reservations with the Highways Agency, ' Larkin reports.

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