Known in Europe as the step barrier, the new design uses less longitudinal steel and needs a much shallower embedment in the road surface than the current generation of vertical concrete barriers (VCB) that have been used successfully on limited sections of the UK motorway network. Formal approval of the new design will come when it is included in the next edition of the Highway's Manual of contract documents for highways works. Until then, use of the new barrier will require a Departure from Standard to be issued by the Highways Agency.
Developed in Holland, the concrete step barrier is widely used throughout mainland Europe where it has proved successful in preventing that most dangerous of motorway accidents: the crossover. This is where central barriers have not been able to restrain an errant vehicle from crossing over in to the face of oncoming traffic.
In the UK crossover accidents account for over 200 motorway accidents a year, many of which cause multiple fatalities.
In addition to containing all cars, 4x4s and small lorries, the new shaped concrete barrier provides an inherent containment level of H2 which can contain an errant 13t vehicle, such as a coach or heavy goods vehicle, compared to the normal containment level of N2 which is designed to cope with vehicles only up to 1.5t.
The step barrier is designed to a similar mass as the current VCBs. But at 900mm, it is 100mm higher than VCBs and fully meets the demanding requirements of H2 certification.
'The concrete step barrier provides greatly superior inherent containment levels. Standard steel and wire rope barriers are limited in the level of containment that they can provide, ' says David Jones, director of Britpave, the transport infrastructure group.
'They can only offer containment up to N2 compared to the much higher H2 level provided by concrete step barriers.'
Unlike VCBs, the step barrier features only two strands of longitudinal steel and this can be a cable rather than a reinforcement bar. Furthermore, the barrier does not require the deep embedment of a VCB and this greatly assists construction as only a simple milled trench in the road surface or nominal pavement overlay is required.