Tests showed that a reinforced concrete bridge parapet similar to that erected on an elevated motorway in west London complied with the requirements of technical memorandum no. Be5 in that it contained a vehicle weighing 1530 kg striking at 113 km/h and at 20 degrees. In addition the parapet adequately withstood impacts from a passenger coach weighing 5670 kg striking at 80 km/h and 20 degrees. The transverse deceleration of private cars was reduced from about 8 g to 5 g by using energy absorbing systems either in steel or plastics fitted to the traffic face of the parapet. Damage to the cars was reduced and they were steered back to the parapet after impact. The same energy absorbing systems had less effect on the impacts with coaches although the vehicles were noticeably less damaged. The all-steel energy absorbing system consists of open box guardrail mounted on hexagon-shaped brackets. The guardrail is mounted with its centre 0.61 m above the roadway and is continued beyond the parapet where it can be mounted on knock-down posts to form the safety fence, thereby eliminating the familiar transition problem at the end of the parapet. Details of the system are contained in drawing no. sg1040.27/a obtainable from the transport and road research laboratory. (Author/publisher)
Abstract