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Road sense

CONCRETE ENGINEERING - Tests prove that a newly designed concrete motorway crash barrier could save the lives of many road workers and road users. David Jones reports.

Forty people die every year in motorway accidents that involve vehicles breaking through crash barriers separating traffic lanes. The victims are often drivers or passengers, but can also be people working on the roads. Getting the design of crash barriers right is paramount to reducing the number of deaths each year.

Insitu concrete paving association Britpave recently tested a new barrier design to see how effective it was.

The concrete step barrier was subjected to a range of tests.

Consultant Arup developed computer simulations to look at the impact of different of cars and coaches on the barrier, then dynamic impact tests carried out by Britpave at the Motor Industry Research Association (MIRA) highway and vehicle open-air crash facility verified the results.

The MIRA tests were carried out on both fixed and variable height concrete step barriers, which were unrestrained and required no foundations. A 13t school bus travelling at 70km/h and at 20° to the traffic face of the barrier was chosen as the crash vehicle. The impact point was considered to be the centreline of the bus and a point one third of the way along the length of the test barrier.

Both buses were successfully restrained, controlled and redirected by the barriers, and there was no crossover. Both barriers suffered scratching and chipping, but did not move and the barriers did not penetrate the passenger compartments.

This is because the step had been designed to take the impact of the vehicle wheel and suspension system, and direct the vehicle along the barrier in the direction of traffic fl ow. The smooth 5% angle of the barrier's traffic face is also less damaging to motorcyclists compared to barrier systems which contain protruding bolts and dangerous support posts.

The tests proved that the concrete step barrier can contain vehicles of up to 13t, including coaches, 4x4s and light vans.

Looking further at the concrete barrier design reveals that it is repair and maintenance free over its 50-year life.

Eliminating the need for repair and maintenance eliminates the need for contractors to be working in the middle of motorways.

This is one of the reasons why the Highways Agency now prefers concrete step barriers to steel ones for roads where the average daily traffic exceeds 25,000 vehicles. Other reasons include that the concrete system does not require foundations and that it is quick and cheap to erect.

The Welsh Assembly find The Department for Regional Development Northern Ireland have also followed the Highways Agency's lead and specified rigid concrete barriers for their principal trunk road networks.

Lengths of the new step barrier have been used on the M1, M6, M62, M18, M5 and M180 motorways. It is also being used on a handful of A roads, and to protect columns supporting the new Docklands Light Railway at London City Airport.

David Jones is director of Britpave Details on CD - A CD-Rom, 'Drawings for Concrete Step Barriers and Ancillary Items', containing some 70 technical drawings in pdf format and AutoCAD blocks of principal items for download is available from Britpave via its website www. britpave. org. uk.

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