Engineering better steel barriers: protecting drivers and passengers is not just a function of making safer cars. Engineering safer road barriers matters, too

Automotive Design & Production, March, 2007 by William Kimberley

Roadside restraint systems, or crash barriers, are so much part of the road furniture that they hardly come in for a second look. They are part of the scenery and we expect to see them lining the highways and main roads almost everywhere in the world. However, far from being metal sheets that are attached to metal posts, today's "restraint systems" can be quite sophisticated and well-engineered products. Since 1997, roadside restraint systems in Europe have been required to meet the European EN1317 standard, an amalgam of regulations from the-then 16 member states of the European Union. However, in some cases the new pan-European standard was a dilution of the individual national ones it superseded. "EN1317 was adopted by the European Union countries in 1997 but while it meant there was standardization in roadside restraint systems across the-then 16 countries, it did mean that they were a little diluted from our own BS6779 standard that we had used in the UK until then," says Bill Russell, market and business development manager, Corus Tubes (www.corustubes.com). "However, on a positive note, it did mean that there were prescriptive tests which meant that a system from one country could be objectively assessed against that of another."

Using simulation software, advanced modeling techniques, and physical testing, Russell and his colleagues set to work on developing a new family of roadside restraint systems that they considered ticked all the boxes and challenged the prescribed test procedures within the European standard. "The European EN1317 standard set an important safety benchmark for the industry," says Russell, "but we wanted to go and test it beyond its minimum requirements and understand worst-case scenarios. We wanted to challenge the currently accepted impact test assumption because we discovered that although a roadside safety system could pass the European standard, it didn't necessarily mean that it was safe under all circumstances."

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What he and his colleagues at Corus Tubes found were some anomalies in the European standard. An important one related to the size of vehicle tested against the barrier system. The standard requires manufacturers to test how a barrier performs against the heaviest vehicle within a system class, for example a 30-tonne truck, and then tested against a 900-kg small car to check impact severity. However, there is no formal requirement to test anything in between these two extremes and yet the majority of vehicles on European roads are mid-size cars weighing between 1,400 to 2,000 kg.

"The benefit of using our computer modeling techniques and simulation software meant that we could also easily test our system against a typical 1,500-kg mid-segment car," says Russell. "We felt that this was particularly important as the majority of cars on Europe's roads today are in this mid-range weight category." What he and his colleagues discovered was that when a 1,500-kg car was crashed against a barrier, it was more dangerous to the occupants than either the heavy truck or the lightweight car. This was because the increased impact energy caused more deformation of the crash barriers' mounting brackets, potentially leading to unacceptably high levels of severity in the vehicle passenger cell, so making the system unsafe. This led to their re-designing the barrier to include an energy-absorbing arrangement resulting in a more controlled and progressive deformation and more acceptable severity levels for both small and mid-range cars.

"We developed our systems on an advanced computer simulation system where we were able to develop the 'what if scenarios. 'What if we changed the point of impact, what if we changed the size and weight of the vehicle or what if it did such-and-such during the crash sequence?' These were some of the questions we were able to address without having to resort to real-life tests. This led us to developing the Protect 365 system." This is the new family of roadside restraint systems that Corus believes will mark a significant step forward in performance levels for highway restraint systems, significantly contributing to improved road safety while reducing the number of serious injuries and deaths. Russell and his team worked directly with vehicle manufacturers in the system's development. "Initially we worked with Rover before it had its problems and then we worked with Daf Trucks and Leyland Vehicles." Both manufacturers were prepared to give Russell and his team engineering drawings on forthcoming trucks, 30 and 16 tonnes respectively, which were subsequently modeled for crash testing simulation. "We simulated both vehicles in our programs and then returned the results to the manufacturers who could use the data we supplied from the crash tests to incorporate into their final designs if they so wished."

A major discovery occurred when the development team were evaluating a set of impact test results and found that the Head Impact Criteria (HIC) was far too severe. Although HIC measurements are a recognized automotive industry benchmark used by carmakers, it is not a test criteria currently used in the European standard to define crash barrier safety performance levels. Using fully instrumented crash dummies, Corus tests showed that during impact speeds exceeding 110 km/h (68 mph), occupants heads could come through the vehicle side window and strike the barrier. The resulting simulated HIC value of 2,300 in this scenario was well over twice the 1,000 value targeted by vehicle manufacturers for vehicle development, and would almost certainly equate to serious injury or even death. "As a result of these tests, we realized we needed to modify the design of Protect 365 to include a unique 'step' in the barrier profile shape in order to eliminate this effect and prevent head impact occurring," says Russell. "Subsequent tests on the re-designed barrier have shown a significant reduction of the HIC value to a safe level of 107, well within the automotive industry target levels."