Signalling queries

["Bradley Torr" <truenorth@one.net.au.SPAMTRAP>]

Hello all,

Being only an interested layman when it comes to railway technology - my
railfan interests mainly centre upon the generalities and the political,
geographic and social aspects of railway systems - I don't know much about
signalling, but I'd like to know more about it. To this end, I have several
questions regarding signalling theory and practice.

* What is the difference between 'train order working' and 'staff working'?
I believe that staff working is centred around the idea of 'staffs', which
I have heard being referred to as pegs or tokens, which are carried by
train crews and then placed into a machine at certain points along a line
in order to access the next section of the line.. am I correct?

* What does "CTC" stand for, and what does it mean?

* When a train enters a signalling section, the first set of wheels on a
train make contact with track circuits, which alert the signalling system
that the train is entering a new section. How does a signalling system know
that the train has left the previous section, though?

* I remember, during a journey in an Endeavour from Moss Vale to Macarthur
in February 2000, seeing a sign somewhere around Picton on the Down saying
something like "BEGIN SINGLE LIGHT INDICATION". I also notice that most
signalling here in Wollongong is single light. At which points radiating
from Sydney does double light signalling end and single light signalling
begin?

Thanks in advance for your kind and intelligent and constructive answers.

Regards
BT