> >British system of a Flashing Yellow is used.
> >However, Low Speed indications do differ in that SA allows a Clear Low
Speed
> >whereas such an indication is very rare in Vic. Again the Adelaide
suburban
> >area is different.
>
> One of the aspects of signalling where 2 color light signals are used as
in
> VIC,SA and WA is the concept of a home signal or even an automatic signal
> displaying green over red for clear normal speed.
> What information is the lower red light supposed to be conveying under
> these conditions.In NSW home signals display green over green or simply a
> single green for clear normal speed which makes a bit more sense.
> Its reasonable to display multiple red lights for home or automatic
signals
> where the lights are vertically staggered,but it seems a bit silly to
display
> red lights for clear.
> Anyone know the history or logic if any of these indications?
>
In Vic , SA etc the top light indicates a normal speed signal and the lower
light indicates a medium speed aspect. It follows that a third, smaller
light indicates a low speed signal. Thus, in vic the sometimes fixed lower
red light indicates that the indication above is a normal speed not medium
speed requirement. On some signals the top red light is fixed indicating
that all moves are at medium speed.
In NSW the top light indicates the conditions between that signal and the
next in advance, while the lower light tells you what to expect on the next
signal. Green over Green indicates that the signal section is clear and the
next signal has a proceed aspect. Green over Yellow indicates that the
signals section is clear but the lower yellow warns that the next signal
has a caution aspect. Green over Red indicates that the signal section is
clear but the lower red light indicates that the next signal is at stop.
> Also is there any differances in interpretation between a red over red
> indication and a single red,ie single color light signal with no lower
> light,as the down departure signal at Sunbury displays.?
>
> cheers
> MD
If it were a Green over Red the worst the next signal could show is Reduce
to Medium or Normal Speed Warning, because it is a single light signal it
gives no indication whatsoever about the next signal. My guess is that
departing Sunbury on the Down is entering a Double Line Block section
(Block Telegraph in NSW speak) and the next signal is at the next station.
VR classified signals as two position which have one light and usually two
indications and three position which have two lights and up to seven
indications.
For some odd reason they are paranoid about mixing types of signals at the
same station but it does happen at odd location like Melton where the yard
is two position lights and is approached on a CTC (three position)
mainline. It is common here to get a Yellow over Red on the approach auto
followed by a Green at the outer home and a RED at the Home Arrival.
-- Cheers Krel"Any sufficiently advanced technology is indistinguisable from magic" - Clarke's Law