Crash tests prove unrivalled performance of concrete step barriers

The tests were carried out at the Motor Industry Research Association (MIRA) on a surface-mounted, unrestrained concrete step barrier and a surface-mounted, unrestrained variable height concrete step barrier at MIRA's highway and vehicle open-air crash (HAVOC) facility. They were conducted in accordance

with the: guidelines described in EN 1317: 2(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 along the length of the test barrier. The vehicle was intended to impact the barrier at 70km/h, facing the traffic at an angle of 20?.

Test results

Both coaches were successfully restrained, controlled and redirected by the barriers. There was no crossover. Both lengths of barrier suffered some scratching and chipping but neither suffered from 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 results proved concrete step barriers do not require costly foundations or restraints and yet still meet the necessary requirements. Importantly, neither of the tested barriers demonstrated the need for repair.

The tests fully vindicate the decision by Highways Agency in January 2005 - recognising the increased safety, lack of ongoing maintenance and improved cost benefits to issue TD 19/06 stating that the concrete step barrier, rather than steel barriers, should be installed on all motorways where the average annual daily traffic (AADT) exceeded 25,000 vehicles per day. The Department for Regional Development in Northern Ireland has followed the Highways Agency's lead and specified the rigid concrete barrier for its principal trunk road network.

Development of the barrier

First developed in Holland, the concrete step barrier is effective in preventing that most dangerous of motorway accidents: the crossover. This is where the central barriers fail to restrain a vehicle from crossing over into the face of oncoming traffic. In the UK, there are over 400 crossover motorway accidents a year, resulting in more than 40 deaths. With a containment level of H2, the concrete step barrier is fully able to contain vehicles of up to 13 tonnes such as coaches, 4 ? 4s and light vans. In comparison, the steel barriers that currently serve the motorway central reserve have a containment level of N2, which is only able to contain cars weighing up to 1.5 tonnes. The new step barrier conforms in every respect to the requirements of the European Standard 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 barrier 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 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 on average three times during this period, but would also need regular tensioning and maintenance. The Highways Agency is committed to a strategy that reduces the risks faced by road workers; therefore, by eliminating the need for repair and maintenance, the requirement for contractors to be exposed to potential danger by working in the middle of motorways is removed.

Concluding remarks

Lengths of new step barrier have been installed on the M62, M18, M180, Ml, M5 and M6 motorways. One project has also been completed on the A12 trunk road and another will soon start on the A27 - both of these are Highways Agency roads. Short lengths of concrete step barrier have also been installed on the Al in Nottinghamshire, A55 in North Wales and are providing protection to the columns supporting the new Docklands Light Railway at London City Airport. The installation of concrete step barriers is predicted to increase dramatically now that their minimum maintenance and long-term performance benefits are recognised.