The introduction of TPWS, Train Protection Warning System, across the national network has resulted in these small grids appearing between the rails on the approach to signals, speed restrictions and terminal stations. Two grids are normally placed, one to arm the on-train systems and one to activate the system. The grids are placed at a suitable distance apart for the expected speed of trains, such that if a train approaching a restrictive signal has not reduced speed the system will automatically trigger a brake application.
Each pack contains 12 finely moulded grids, plus an appropriate number of supporting bars, allowing these to be trimmed to fit specific locations and track fixings.