Crash tests prove unrivalled performance of concrete step barriers

The tests were conducted in accordance with guidelines described in BS EN 1317(1). For both the step barrier and the variable step barrier, a 13-tonne single-deck coach was used with the impact point being selected as the centreline of the coach aligned to a point approximately one third of the way

The results

Both couches were successfully restrained, controlled and redirected by the harriers. There was no crossover. Both lengths of barrier suffered some light damage but did not suffer any movement or detachment of any significant parts. There was no penetration on the passenger compartment of either coach by any part of the barriers. The test results show how effective the stepped design of the barrier is in reducing the effect of impact forces on vehicle occupants. Furthermore, the success of the surface-mounted barriers has advantageous cost implications as they proved that concrete step barriers do not require costly foundations or restraints and yet still provide a containment level rating of 'H2 W2'.

The tests fully vindicate the decision by the Highways Agency to issue Interim Advice Note 60/65 stating that the concrete slep barrier should be installed on all motorways where the average annual daily traffic (AADT) exceeds 25,000 vehicles per day. The Department for Regional Development Northern Ireland have also specified rigid concrete barriers tor their principal trunk road network. Barrier benefits

First developed in Holland, the concrete step barrier is effective in preventing crossover accidents. This occurs when the central barriers fail to restrain a vehicle from crossing over into the lace of oncoming traffic. In the UK, there are more than 400 crossover motorway accidents a year, resulting in over 40 deaths. With an H2 containment level, the concrete step barrier is fully able to contain vehicles up to 13 tonnes, such as coaches, 4 ? 4s and light vans. In comparison, steel barriers have a containment level of N2. which is only able to contain cars up to 1.5 tonnes. The new step harrier conforms in every respect with the requirements of BS EN 1317.

Significantly, the concrete step barrier meets the European requirements for passenger protection in the event of a car impacting the barrier. The 'step' of the concrete harrier has been designed to take the impact of the vehicle wheel and suspension system and directs the vehicle along the barrier in the direction of traffic flow, thus minimising injury to occupants. The smooth 5% angle of the barrier traffic face is also less damaging to motorcyclists compared with other barrier systems with protruding bolts and dangerous support posts.

The concrete barrier is designed to be repair- and maintenance-free for the entirety of its 50-year life. By contrast, steel barriers, with a design life of only 20 years, would not only have to be replaced three times during this period but would also need regular tensioning and maintenance. Eliminating the need for repair and maintenance reduces the requirement for contractors to work in the middle of motorways. The Highways Agency is committed to a strategy that reduces the risks faced by road workers and the decision to install concrete step harriers forms part of this strategy.

Concluding remarks

So far, lengths of new step barrier have been installed on the M62, M18, M180, M1, M5 and M6 motorways. One project has also been completed on the A12 and another will soon start on the A27 - both are Highways Agency roads. Short lengths of concrete step barrier have also been installed on the A1 in Nottinghamshire, A55 in North Wales and are providing protection to the columns supporting the new Docklands Light Railway at London City Airport.