S.P.A.D. Signals (UK Rail Question)

[Prince271088]

I was looking over the use of S.P.A.D. Signals and the information I have states that one should be placed about 50m after a signal, which if passed at danger could cause serious conflict. I understand that in it's initial meaning but what is defined as serious conflict prototypically?

I get that for instance where two tracks diverge into one track would be the main example of this occuring (?) but for example what happens at a crossover or junction because to my knowledge there aren't that many S.P.A.D. signals on the network?

Basically could someone explain when I should be using a S.P.A.D. signal other than at the example of two tracks merging into one and on a different note, also what protections are in place at crossovers to prevent similar sorts of things happening?

Thanks in advance

 

[edh6]

http://www.railsigns.uk/sect8page2/sect8page2.html

Following a series of high-profile accidents resulting from SPADs, the 'SPAD indicator' was introduced as a secondary warning device, to be placed ahead of selected 'high risk' signals. The signals involved have often tended to be platform starting signals that protect junctions. In normal circumstances, a SPAD indicator is unlit, but will be activated in the event of an associated signal being passed at 'danger'. When activated, the original form of indicator displayed the word "stop" vertically in red illuminated letters, with flashing red lights above and below [8.30]. Only two examples of this type were ever installed, the first beyond signal S198 at Meadowhall in October 1994 and the second beyond signal L293 at Maryland in April 1996. Later SPAD indicators installed in 1996 were based around a conventional three-aspect colour light signal head, with a distinctive blue backboard to avoid them being mistaken as defective colour light signals when unlit. All three lenses were red, and the middle one had the word "stop" written across it. When activated, the top and bottom lights flash, and the middle light shows a steady red [8.31]. Further installations made from 1996 onwards omitted the word "stop" on the middle lens [8.32]. Since the introduction of the Train Protection & Warning System (TPWS), which can intervene to stop a train, very few new SPAD indicators were provided and some existing examples have been removed.

 

[Prince271088]

Considering I use that site quite a bit, I should have looked there first... thanks