A-Lights

At first glance A-Lights are rather uninteresting. However, a more detailed look reveals that there is more to them than meets the eye. The lights have become even more interesting with the recent introduction of Arrival signals in Track Warrant Territory and their use on intermediate signals to facilitate rescues and resetting axle counters.

In this page I explain how A-Lights are used, provide excerpts from relevant regulations, and give some examples of signals with A-Lights.

See also my Subsidiary Lights and Petone A-Lights pages.

A-light in detail



Regulations for Automatic Signalling with Three Position Upper Quadrant Semaphores and Colour Light Signals 1927

To understand the A-Light I find it useful to go back to basics in the 1920s, when Automatic signalling was introduced into New Zealand.

Classes Of Signal:  

  • Automatic. Controlled by track circuits; not manually controlled.
  • Absolute Automatic. Controlled by track circuits; not manually controlled.
  • Interlocked Automatic. Controlled by track circuits and also manually controlled.

Purpose of an A-Light:
Converts an Interlocked Automatic signal to an Automatic signal when a signal box is switched out.

Regulation 13:  
Authorises a train to pass an Automatic signal at Stop under similar conditions to a Stop and Proceed signal in the rules applicable in 2012.



Comparison With 2012:
Note that the terms Stop & Proceed and Stop & Stay are not used in the 1927 Regulations and also that there is no reference to correctly set points.

Alights in 1927



Switchout - The 1988 Rule Book Definition

The traditional switch-out signal box explanation of A-Lights in the 1998 rule book is consistant with the 1927 interpretation. The actual situation in 2012 is more complex and is covered later on this page. Note that switch-out signal boxes are a dying breed and it is possible that in a few years the situation described here may be of historic interest only.


At some stations where the points are only occasionally used the signal box may be switched In or Out. In such cases the Stop and Stay signals at the station are equipped with an additional light unit placed below and to the right of the lower unit or Marker light/disc as the case may be. The additional light unit displays no light when the station is switched In, but when the station is switched Out it displays an illuminated letter "A", visible at short range only. (See figures on the right). "A" lights are backed by a triangular metal plate painted black with a white border.

When an illuminated letter "A" is displayed on a Stop and Stay signal the signal concerned is classed as a Stop and Proceed signal and the rules and regulations applicable to Stop and Proceed signals apply to it. See my Signal Classification page for details of signal classes.

"A" lights are also provided on Intermediate Stop and Stay signals protecting points and crossover roads at double-line switch-locked sidings.

Note that in the rules there is no mention of correctly set points.




A-Lights in 2012

To understand an A-Light in detail it is necessary to refer to both the Rule Book and the Local Instructions for the area. These are the rules and instructions applying in 2012. The 2012 rules are consistant with those in 1927; the Local Instructions extend the meaning.

Rule Book


An illuminated A-light means:

Double Line Automatic Areas:

Station switched out, or Double Line switchlock siding closed.

Signal classification changed from Stop & Stay to Stop & Proceed.

There is no reference to correctly set points.


Arrival Signals TWC in areas:

When the "A" light is extinguished TWC Arrival signals become Stop and Stay signals.

The 'A' light means the signal is under automatic control rather than the station being switched out.

The "A" light illuminated indicates that the motor points are correctly set and secured for either the mainline, loop or branch line but not necessarily that the route is unobstructed. This is an extension of the 1927 regulations.

Wellington Local Instructions


Points Locked. In the Wellington - Plimmerton and Wellington - Trentham Double Line Automatic Signalling areas an "A" light indicates that the main line points up to the next signal in advance are so secured that the train may pass safely over them. If a signal with an "A" light is at "STOP" and the "A" light is lit, the main line points in the section ahead are correctly set and secured but the track may be occupied.

Intermediate Signals. Between Paekakariki and Waikanae Stop & Stay Intermediate Signals may be equipped with A-Lights. The A-lights will only be illuminated (converting the signal to Stop & Proceed) when set by Train Control for:

  • Axle counter failure and reset "sweep" required
  • Entry to occupied section to assist a disabled train beyond Intermediate signal, following service to push disabled service through the section
  • Automatically illuminate following a communications failure.

A-Light Controlled By Track Circuit.  At Taita, Porirua and Plimmerton when the section in advance of the Up Home signal is occupied the A-Light on the Home signal goes out. This prevents a closely following train entering the section under Stop and Proceed rules, which would prevent a terminating train "pushing up" and returning to Wellington.




Examples Of A-Lights

A light on platform starter

14 Up Platform Starter at Petone. The Up Main is switched out and the signal is Stop & Proceed.

If this signal protected points (which it no longer does) they would be set and locked for the main.

A-light on intermediate

4178 intermediate signal on the Up Main at McKays is Stop & Stay with the A-light normally off. Control can turn the A-light on, converting the signal to Stop & Proceed.

I will add a better photo of this class of signal when I can locate one that can be photographed legally from the approach side.

A-light

1489 Intermediate signal protects Woburn North Siding. The points are operated by electrically locked high-column switchstands. The illuminated A-Light proves that the points are locked normal and indicates that the signal is Stop & Proceed.

When the control box door is opened the signal goes to Stop and the A-Light goes out, converting the signal to Stop & Stay.




Passing A Signal At Stop - 1927

The following regulations are from the Regulations for Automatic Signalling with Three Position Upper Quadrant Semaphores and Colour Light Signals. They define how Interlocked Automatic and Automatic signals can be passed at Stop.

The following does not apply if the signal is classed as a Departure signal.

8. TRAIN STOPPED AT INTERLOCKED AUTOMATIC SIGNAL.

(a) In the event of a detention at an Interlocked Automatic signal as described in Regulation 1, clauses (i) and (j), the Driver must, on ascetrtaining that the cabin is switched "Out" and the "A" light not illuminated, and seeing that the yard is clear, draw his train forward to the next signal, under the control of a Pilot, who should be the Guard or Fireman of the train in question.

(b) When it is required to allow a train to pass an Interlocked Automatic signal at "Stop" for the purposes of rendering assistance to a disabled train, the Driver must be accompanied by the Guard of the disabled train, or by the Fireman in the case of a disabled light engine, who will act as Pilot.

(c) On single lines no departure signal may be passed at "Stop" except under the special instructions laid down for passing signals at "Stop" for single-line working (Regulations Nos, 29, 38, 39, 40, 42, and 44).

The following does not apply if an Interlocked Automatic signal, with illuminated A-Light, is classed as a Departure signal.

13. TRAIN STOPPED BY AUTOMATIC SIGNAL

(a) Should the driver find an Automatic signal at "Stop" he must bring his train to a stand and wait at such signal ten seconds. Unless he is aware that the section ahead is occupied (see clause (b) ), the Driver may,if, at the expiration of ten seconds, the signal is still at "Stop", proceed cautiously past the signal, being prepared to find the section occupied, obstructed, or a broken or misplaced rail.

After passing an Automatic signal at "stop" the Driver must continue to excercise great caution when passing through the section, and even though the signal next in advance may be seen to be at "Clear" or "Caution" he must nevertheless be prepared to stop clear of any obstruction until he arrives at such signal. In foggy weather or when a good view of the line ahead cannot be obtained the Driver must not rely on the number of minutes that a previous train is supposed to be ahead of him, but in all cases must regulate the speed of his train so as to enable him to stop within the distance he can see ahead. If on arrival at the next signal it is at "Caution" or "Clear", the Driver may proceed accordingly. If, however, it is also an Automatic signal and is at "stop", the same procedure must be observed.

Note. - It must be distictly understood that the passing of a "Stop" signal, as herein permitted under special cirumstances, applis only to an Automatic signal and not to any Absolute Automatic or Interlocked Automatic signal excepting as provided in Regulation 1,clause (j).

(b) If after passing a "Stop" signal the Driver becomes aware that the preceding train is in the section he must at once bring his train to a stand and except when verbaly instructed by the Guard of the preceding train to draw cautiously forward, must wait until the train in front had proceeded on its journey.

When two trains are in any section at the same time the Driver of the second train must, after the front train has proceeded, follow at such a distance as will enable him, to avoid colliding with the front train in the event of it again being stopped, and he must bring his train to stand at the next signal if at "top", and then proceed in accordance with Regulations 8 and 13.



Passing A Signal At Stop - 2012

The following regulations are from the 2012 Double Line Automatic Signalling Regulations. Similar regulations are in the Single Line Automatic and CTC regulations.

2. Train Stopped at Stop and Stay Signal

(a) Stop and Stay Signal Equipped with an "A" Light - If detained detained at a Stop and Stay signal equipped with an "A" light, and the "A" light is not illuminated, the Locomotive Engineer after ascertaining that the signal box is switched Out (or, in the case of a switch-locked siding, that the switch lock is locked), and upon observing that the line is clear, must cautiously move the train forward to the next signal.

Failure of Signals leading over Motor Points
The provision of Rail Operating Procedures Section 11, for failure of signals leading over motor points must be followed.

(b) Intermediate Stop and Stay Signal - If a train is detained at an Intermediate Stop and Stay signal which is not equipped with an "A" light the Locomotive Engineer (or a member of the train crew so instructed by the Locomotive Engineer) must communicate with Train Control. Train Control, after being satisfied that the section ahead is not occupied, may authorise the train to pass the signal at "Stop".

If an Intermediate Stop and Stay signal has been passed at "Stop" Train Control after being satisfied that the section ahead is not occupied may authorise the train to proceed.

Note-In connection with the passing of these signals Locomotive Engineers must ensure that the train proceeds cautiously, being prepared to find the section obstructed or displaced rail or points wrongly set and must not assume that any obstruction is protected. Level crossings in the section equipped with automatic warning devices must, also be aproached with caution as the alarms may not operate correctly.

If the signal next in advance is observed to be at "Caution" or "Clear" the Locomotive Engineer must not relax vigilance but must until he reaches the signal be prepared to stop the train clear of any obstructions.

Failure of Signals leading over Switch locked siding points:
When a movement is detained at an Intermediate Stop and Stay signal protecting a switch locked siding and the "A" light is extinguished:

  • Train Control may authorise the movement to proceed cautiously forward after ensuring the line is clear,
  • The Locomotive Engineer must stop short of the switch locked points concerned and check them to ensure they are correctly set and secure for the movement to pass safely over them.

3. Train Stopped at an Intermediate Stop and Proceed Signal

(a) When a Locomotive Engineer observes a Stop and Proceed signal at "Stop" he must stop the train; if, at the expiration of 10 seconds, the signal is still at "Stop" the train may proceed cautiously past the signal, the Locomotive Engineer being prepared to find the section occupied or Obstructed, points wrongly set, or a broken or displaced rail.

Where there are points in the section ahead of a Stop and Proceed Signal which has been passed at "Stop" the Locomotive Engineer before the train passes over the points, must examine them and see that they are so secured that the train may pass safely over them.

(b) After passing a Stop and Proceed signal at "Stop" the Locomotive Engineer must not assume that any obstruction in the section is protected, but must regulate the speed of the train so that it can be stopped within the distance he can see ahead and clear of any obstruction.

Note-In connection with the passing of these signals Locomotive Engineers must ensure that the train proceeds cautiously, being prepared to find the section obstructed or a displaced rail or points wrongly set and must not assume that any obstruction is protected. Level crossings in the section equipped with automatic warning devices must also be approached with caution as the alarms may not operate correctly.

If the signal next in advance is observed to be at "Caution" or "Clear" the Locomotive Engineer must not relax vigilance but must, until he reaches the signal, be prepared to stop the train clear of any obstructions.

(c) If, after passing a Stop and Proceed signal at "Stop", a Locomotive Engineer becomes aware that there is a train stopped in the section he must stop his train and except when verbally instructed by a responsible member of the crew of the train in front to draw cautiously forward, must wait until the train has proceeded on its journey before again starting his train.

If, however, the train is observed to be moving through the section the second train may follow it at a safe interval.

Note-In view of the possibility of a train which has passed a Stop and Proceed signal at "Stop" being in the same section as another train, strict attention to and observance of tail lamps after dark, or when visibility is bad, is of the utmost importance.



Tue Jan 1 08:20:33 NZDT 2013

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