Very generally, and not pretending to be running a Rules or signal design class
here: Interlocking signals are used to protect places where tracks meet or
cross. They can be set specifically for each movement by an operator either
locally or remotely, or they can be triggered to operate automatically to clear
a route for each train approaching, blocking any other train arriving on a
different track until the first has passed. The control mechanisms for the
signals and switches are interlocked mechanically, electrically or
electronically in such a way that a signal cannot be cleared unless there is a
safe route through the interlocking zone. This means all switches (if any) must
be set for the train to move through on the intended route, and there are no
other routes cleared which would conflict with it. Once a signal has been
cleared, the switches on the route, and all signals governing potentially
conflicting routes, are locked in place until the train has gone through (or
the signal has been set to STOP and a timer runs out). Not all interlockings
have switches, as they can also be used to govern diamond crossings. But they
must all contain signals. An interlocking can involve a simple diamond crossing
or a junction of two tracks, or it can be a complex beast with a spaghetti bowl
of crossovers. Under Interlocking Rules, a STOP signal is absolute and trains
must not proceed after stopping without explicit permission. The default state
of an interlocking signal is STOP unless cleared to a less restrictive
indication.
Block signals exist to protect trains that are not going through junctions. In
their simplest form they protect trains from running into the rear of a train
ahead of them. Automatic block signals are activated electrically by the
presence of a train, altering an electric circuit flowing through the rails.
(There are manual block signal systems, and other manual block systems, which
are not relevant to your question.) Under ABS STOP AND PROCEED is normally the
most restrictive signals, normally meaning proceed no more than 15 mph and
prepared to stop short of obstruction, opposing train, broken rail etc.
(Remember this is not a rules class.) However ABS also allows absolute STOP
signals. A simple ABS system is unidirectional and is used on a double track
railway, with the current of traffic in opposite directions on the two tracks.
Absolute Permissive Block (APB) signals allow ABS to function in both
directions on a single track without head-on collisions or serious delays. APB
provides absolute signals at the end of sidings or double track. These are set
to STOP when an opposing train enters the other end of the section, forcing a
train to wait there until the opposing train has gone past. Along the single
track the signals are permissive, i.e. STOP AND PROCEED allowing trains in the
same directions to follow each other. These intermediate signals work the same
way as simple ABS signals. The default state of an automatic block signal is
CLEAR unless a train in a nearby block sets it to a more restrictive
indication. Interlocking signals are wired to work like block signals so the
presence of a train will override a less restrictive indication the signal
would otherwise be set to.
Block signals do not convey authority to operate a train. They are overlaid on
the system of written authority used on the railway.
Centralized Traffic Control (CTC) combines some features of interlocking and
block signals. Controlled points such as junctions, siding ends, end of double
track, or crossovers between two or more tracks, are controlled by a dispatcher
or rail traffic controller. These technically are interlockings. The signals on
the main track or tracks between these points are technically automatic block
signals. They are controlled solely by the presence of a train rather than by
the operator. (The controlled signals are also overridden by the presence of a
train on adjoining blocks.) The indications in CTC are consistent with those in
ABS and interlocking rules. The big difference is the rules governing CTC. CTC
signals themselves constitute the authority for train movement within CTC
territory.
For the most part, CTC signals at junctions will look and behave like
interlocking signals, and CTC signals between controlled points will look and
behave like block signals.
Block signals in ABS generally have one or two heads. In ABS a two head signal
will normally have the heads staggered to indicate they are permissive. However
if there were a two head signal at a siding end under APB, the heads would need
to be vertical to indicate it is an absolute signal. Interlocking signals may
have one, two or three heads. Signals protecting diverging routes would
normally have at least two. A single head interlocking signal would need an “A”
sign to show it is absolute, and a two head signal would have to be vertical
rather than staggered to show it is absolute. A three head signal can only be
absolute; it cannot give a permissive STOP AND PROCEED indication. Dwarf
signals can have only one or two heads even within interlocking limits.
As far as what side of the mast the signals are placed, I would suggest you
research prototype practice for the locations you are interested in. The only
restriction is that a two head permissive signal must be staggered, and as far
as I know the higher head must be to the left and the lower head to the right.
As I warned at the outset, this is neither a rules class nor a signals
symposium. People with rules cards and signal specialists can correct me ten
ways from Sunday. I am just offering the quick and dirty layman’s 25 cent tour
of the subject to give you a quick grounding. There are lots of better sources
on line which can give you more insight.
Don
From: cpsig@xxxxxxxxxxxxxxx [mailto:cpsig@xxxxxxxxxxxxxxx] On Behalf Of Steve ;
Turner
Sent: November-26-13 12:43 AM
To: cpsig@xxxxxxxxxxxxxxx
Subject: RE: [cpsig] What side of mast for signal target
Thanks Don.So if the lights are in line vertically you can have the targets RHS
or LHS of the mast. What would determine what side of mast you position them?
Is there shall we say a default side?. Upon more reading etc I found out to
since I model to mid 60s I should be using UCOR rules not CROR rules. Do you
have a quick summation as to when use interlocking or block type signals………..i
am a bit confused on interlocking terminology? This is very indepth subject and
being an old fart I am getting a bit flustered. Thanks for your help its
greatly appreciated.Steve
From: cpsig@xxxxxxxxxxxxxxx [mailto:cpsig@xxxxxxxxxxxxxxx] On Behalf Of Don ;
Thomas
Sent: November 25, 2013 10:53 PM
To: cpsig@xxxxxxxxxxxxxxx
Subject: RE: [cpsig] What side of mast for signal target
Position of the signal lights on either side of the mast does not affect signal
aspects, so long as they are all on the same side. What does matter is when
there are two lights which are staggered. When in this position, two red lights
mean the signal is permissive and indicatse STOP AND PROCEED. When the lights
are aligned vertically then two red lights mean the signal is absolute and
indicates STOP (i.e. stop and stay).
Don
From: cpsig@xxxxxxxxxxxxxxx [mailto:cpsig@xxxxxxxxxxxxxxx] On Behalf Of ;
sfturner@xxxxxxx
Sent: November-25-13 8:46 PM
To: cpsig@xxxxxxxxxxxxxxx
Subject: [cpsig] What side of mast for signal target
Guys i have been fumbleing my way through the CROR aspects for signal lights
making some model signal lights.I was using the 2007 trackside guide for
location of targets on mast.For instance rule 405 shows green and red target
below and above each other on the RHS of mast yet when i look at other material
this rule and others shows targets on the LHS of mast. What am i missing here
and need to know?. I noticed a few of the materials i was researching showed
targets on opposite sides to the 2007 guide and other materials i was reading.
Not sure and do not want to assume that targ ets vertically placed can be
placed either left ot righthand side of mast. I think i am missing some info
here. .Thanks for any insight to my question. I have gone and made one stand
with vertical aspects ot targets on the RHS of the mast and dont know if thats
correct.Thanks steve
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