The purpose of transitions is to provide a gradual change from the first to the second barrier, to prevent the hazards of and abrupt variation. A transition is designed to connect two specified barriers. The length of a transition is the distance between the ends of the two barriers connected by the transition.
In the early days of vehicle restraint systems, safety barriers were connected to bridge parapets without an intermediate transition.
One of the common methods used to connect steel parapet systems to Open Box Beam safety fence was a tuning fork connector which later became known as the GA 38 and GA 120.
The tuning fork connecter consists of two pairs of plates welded to a length of Rectangular Hollow Section, which pass over the bottom two rails of the parapet and are bolted through to secure the connection. Two fishplates are welded on the other side to receive the adjacent open box beam.
The layout of GA 38 was a very soft system with a lower lateral stiffness than the steel parapet that it was being connected too. This created a hard spot at the end of the parapet. Therefore, a vehicle impact with the safety fence prior to the parapet connection would result in the safety fence deflecting to such an extent that the vehicle would hit the end of the parapet head on. This resulted in excessive crushing of the vehicle with huge deceleration forces being transferred to the occupants of the vehicle with the likely effect of a serious injury or even death.
In order to alleviate the problems associated with the GA 38, the GA 120 was developed. The difference between the two systems being that the GA 120 had closer post spacing's and it contained a rubbing rail beneath the open box beam. This alteration stiffened up the system considerably and eliminated the problems of pocketing inherent with the GA 38 layout. Unfortunately, the system was now too stiff, which meant high levels of energy were being transferred to the occupants during a vehicle impact with life threatening consequences.
The aluminium equivalents were the GA39 and GA140 with other variants referring to different aluminium systemsWhilst the parapet connections differed to the tuning fork arrangement of the steel systems, the open box beam safety fence had the same configuration and suffered from the same failings.
In 2005 the GA 38 and GA 39 and all derivatives were withdrawn from service due to their obvious short comings.
The European standard EN 1317 covers Transitions in part 4 and although not yet published, has been embraced by the UK’s Highways Agency and the National Roads Authority in Eire. The purpose of transitions is to provide a gradual change from the first to the second barrier, to prevent the hazards of an abrupt variation. A transition is designed to connect two specified barriers. The length of a transition is the distance between the ends of the two barriers connected by the transition, as shown below
Tranzflex has been successfully tested as a transition between Varley & Gulliver's bridge parapets and sister company Hill & Smith’s FLEXBEAM safety barrier to EN 1317.
By selecting Varley and Gulliver you have piece of mind, knowing that it is us that takes the liability for product performance.
Don’t get caught out, a transition is required to interface between two safety barriers of different cross section or lateral stiffness.
There are on the market approved Parapets, Safety Barriers and Transitions that when connected together
DO NOT create a fully approved solution because they were not tested together