Re: Signalling queries

[Eddie Oliver <eoliver@efs.mq.edu.au>]

Bradley Torr wrote:


>  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.

Pity there aren't more people with a similar willingness to learn.

> * 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?

More or less. Electric staffs are placed into "machines". There are a
number of identical staffs (e.g. 36 or 50) for a given section, but only
one of these can be released for use at any one time. 

In ordinary train staff and ticket working, there is only one staff for
a section; when not in use, it lives in a box at either end of the
section, but also in the boxes are bits of paper called "tickets". If
more than one train is to pass through the section in one direction
before one goes the opposite way, the first train(s) carries a duly
written-out ticket after the driver has seen that the staff is at the
correct end of the section; the final train in that direction physically
carries the staff through the section.

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

Centralised traffic control, i.e. signalling covering several locations
controlled from a single location (e.g. the NSW north coast line as far
as Casino is controlled by CTC from Broadmeadow).

> * 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?

Because the last track circuit in the previous section is no longer
occupied. 

When you talk about "making contact" with track circuits, that's not
really the right concept. A train "occupies" a track circuit by the
wheelsets making connection across the rails. So when there is a
wheelset anywhere within the length of a given track circuit, that
circuit is "occupied", and the signalling system responds accordingly by
logically recognising that that wheelset (or wheelsets) represent an
obstruction of that length of track.
 
> * 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?

Between Sutherland and Waterfall; Campbelltown; between Penrith and Emu
Plains; Berowra. However there are a few double light areas on the south
outside the suburban area, mainly in areas where upper quadrant signals
still exist in substantial numbers.