Signal Types.
Collectively all stop and distant signals on mains lines are known
as running signals. These signals control the safe running of
trains up and down the main lines.
The Great Western Railway’s standard stop signal was 4ft by 1ft
(See fig. RS1) or 5ft by 1ft if the signal was to be mounted over
26ft above height of the rails. 3ft arms were used inside loops
and sidings to make them distinguishable from signals on the
main lines. The front of the stop signal was red with a white
stripe and the back was white with a black stripe, this was so
drivers could tell which side of the signal they were viewing. At
night a lamp shone through a spectacle glass which was red
for danger/stop and green for all clear. When a stop signal was
cleared it meant that the line was guaranteed to be clear up to
the next running signal.
Distant signals were sized in the same manor as stop signals,
originally these signals were also painted red with a black
chevron and a v-shape notch cut in the end. At night these
signals gave the same light aspects as stop signals so a driver
had to rely on his memory to decide what signals were distant
signals and which were stop signals. (See fig. RS2) This
practice lasted up to 1917 when the Board of Trade required all
companies to make their distant signals more recognisable, it
was agreed that this would be done by painting all distant
signals yellow with a black chevron on the front and white with
a black chevron on the back, they also kept the v-shaped notch
cut out of the end (See fig. RS3). It was not until 1933 that the
GWR had replaced all their distant signals. At night the new
type distant signal shone yellow for danger and green for clear
meaning drivers no longer had to rely on their memories to
decide between a distant signal and a stop signal. A distant
signal when cleared mean that the line is clear into the next
section, i.e. for a signalman to be able to clear a distant signal
all stop signals for the route must be in the cleared position.
The distant signal being clear gives the driver an indication that
he can maintain full line speed.
Running signals on goods loops were normally smaller 3ft arms
with a white ring on them to differentiate them from normal
running signals. (See fig. RS4)
At junctions a bracket signal was used, each signal on a
bracket represented a different route and there would be as
many signals as routes. The route to which each signal applied
would be read from left to right, i.e. the left hand signal
applied to the left hand route, etc. If a diverging route had a
lower speed limit than the main route, the signal arm would be
mounted on a lower post to remind the driver. (See Fig. RS5)
If the signals were at equal heights then the same speed limit
applied to both routes.
Running Signals.
Fig. RS1 - A GWR Standard 4ft wooden running signal.
Subsidiary signals were used within the station limits to signal for shunting moves and for special
purposes. Subsidiary signals do not guarantee that the line is clear to the next signal, they give
permission to pass a running signal at danger but the driver must proceed with caution and be
prepared to stop short of any obstruction and he may only proceed as far as is needed for the move
he is undertaking.
There are several types of subsidiary signals, below are examples of GWR types and their purposes.
Subsidiary Signals.
Shunt-Ahead Signals.
Shunt-Ahead signals, as the name might infer, were used when a
shunting move was required to pass a running signal, normally into
the section ahead, to be able to set back into a siding. When the
section signal was not placed far enough from a set of point these
signals were used to give the driver permission to move his train
forward enough so the rear most vehicle could clear a set of the
points so enabling the points to be changed and the train to be put
into a siding or yard without the need for the whole block section to
be occupied for a short move.
GWR Shunt-Ahead signals were originally a 3ft signal painted red
with a white S fixed to the arm. (See fig. SS1) These were
gradually replaced with the more modern type, a 3ft steel arm
which was painted white with two horizontal red stripes top and
bottom. (See fig. SS2) When these signals were cleared they
revealed an S painted on a white glass background. At night a red
light meant danger and a clear/white light meant clear, when
cleared a lamp shone through the white glass illuminating the S
behind the signal arm.
Calling-On Signals.
These signals were used to enable what is know as permissive
working, (see types of working section for more details), they were
used to enable more than one train to be on one track at a time.
Mostly they were used at stations where more than one train could fit
on one platform, if one train is already occupying one end of the
platform these signals enable another train to pull up carefully behind
it. The signalman had to bring the train to a stop at the signal before
he could clear a Calling-On Signal this was to make sure the driver
knew that the line ahead was occupied and he had to proceed with
care.
GWR Calling-On signals were originally a 3ft wooden arm that had the
letters C O painted in white on it, the light spectacles were inside the
arm. (See fig. SS3) Latterly they employed the same pattern as the
new type Shunt-Ahead signals but when cleared the arm revealed a C.
(See fig. SS4) At night a red light meant danger and a clear/white
light meant clear.
Warning Signals.
Warning signals were used when a train had been accepted under the Warning Arrangement, this basically
meant that the block section was clear only to the home signal of the next signal box and the driver would have
to stop at this signal, he was alerted to this normally by the signalman stopping him at the section signal and
then showing him a green flag or light at night. The driver would acknowledge this with a short blast on the
whistle and then the signalman would clear the signal, the driver knowing he would need to be prepared to stop
at the next signal. In places where this happened a lot or where the section signal was out of sight of the signal
box a special warning signal was provided which meant the signalman would not have to alert the driver specially
every time. Warning signals were also used for entry into goods loops which were normally worked under
permissive working, the warning signal in this case was to alert the driver that there was at least one other train
in the loop. Often there was a selector which would show a number to tell the driver how many trains were in
front of him, giving him an idea of when he would need to stop.
The GWR did not at first use warning signals but had the signalman alert the driver as mentioned above.
Warning signals began to appear along with the new type of Calling-On and Shunt-Ahead signals, they were
again of the same pattern but showed a W when the signal was cleared.
Shunting Signals.
Shunting signals control all shunting movements within station limits
including movements through crossover points and in and out of
sidings. They allow an engine to perform movements not allowed by
running signals, because shunting movements are undertaken at low
speeds the signals do not need to be seen from a far and are normally
placed on small posts on the ground.
The GWR shunting signals were originally much like a miniature version
of normal semaphore signals. (See Fig. SS5) These were eventually
replaced with a white disc which had a red stripe painted horizontally
across it, (See Fig. SS6) the disk was rotated 45° to show a clear
aspect.
In sidings where a headshunt was provided there would often be
found a “Yellow Disc” these took the same form as the normal discs but
had a yellow stripe painted on them instead of red. (See Fig. SS7)
These signals were allowed to be passed at danger providing the route
was set for the headshunt and not on to the main line. This enabled
shunting to proceed in and out of sidings and into the headshunt
without the signalman having to clear the shunting signal each time.
Fig. RS2 - An early type GWR Standard 4ft wooden fixed distant signal.
Fig. RS3 - A later type GWR Standard 4ft Steel fixed distant signal.
Goods Loop/Line Signal
Fig. RS4 - A later type GWR Standard 3ft Steel goods loop / line signal.
Junction Signal
Fig. RS5 - A GWR Junction Signal with Standard 4ft Steel signal arms, the lower mounted signal mounted on the left hand side denotes a reduced speed for the route to which it applies.
Fig. SS1 - An early type GWR Standard 3ft Shunt-Ahead signal.
Fig. SS2 - A later type GWR Standard 3ft Shunt-Ahead signal.
Fig. SS3 - An early type GWR Standard 3ft Calling-On signal.
Left Fig. SS6. This is a later type Shunting signal often refered to as "Discs" it enables shunting movents within the station limits.


Right Fig. SS7. This is a Yellow Disc, a driver is allowed to pass this signal as long as the route is not set for the main line.
Fig. SS5 - An early type GWR Standard shunting signal, this one is currently out of use hence it is paint black all over.