This may sound a stupid question.

At cab signalling block section limit markers on this line there are also what appears to be a subsidary signal (which looks similar to shunt signal) attached to each one, even those on plain line sections with no junctions, crossovers or sidings - what are the purpose of these?

This photo was taken by me at Ebbsfleet International, but these specific markers also have additional indicators as they are at platforms:

Looks like it's an Auxiliary signal:

"On lines with TVM signalling, absolute stop markers (see [2.123]) and shunt markers (see [3.85]) are provided with an auxiliary signal, which is normally extinguished. When 'opened', an auxiliary signal displays two white flashing lights at 45° [9.55]. Clearance of an auxiliary signal authorises the driver to proceed on sight (e.g. during a failure or for admission into an engineering possession). Auxiliary signals can also be associated with conventional signals for use during certain failure conditions. Displaying an aspect known as a 'Proceed on Sight Authority' (PoSA)"

from www.railsigns.co.uk/sect9page3/sect9page3.html and scroll down near the bottom, flashing position signal. Learnt something myself too! Wondered what these were actually as I noticed on Ashford IECC panel that they were on every signal, and thought they can't be just shunt signals!


James.

There's a rule book module giving more details at rgsonline