This is the latest development in the TRL Frangible Pin developed in partnership with British Eventing. At the 2010 FEI Eventing Risk Management Forum it was agreed to trial the use of the frangible pin technology on the reverse side i.e. behind the vertical post. This would allow some lateral movement of the rail as well as downward.
This is the first time I have seen these in action and as you can see instead of employing traditional rope to secure the rail they have used a steel cable to keep the appropriate tension.
I am working on getting some more of the background info on this and the design guidelines when I secure them I will add to the website. Photos thanks to Geoff Sinclair who was CCI 3* TD at the Houghton International event where these were used. The course was designed by Alec Lochore who is Chairman of the British Eventing Safety Committee.