Permissive Working

This page explains the concept of permissive working, particularly as it applies to New Zealand.


(Right) On Wellington Cup Day 26/1/2002 the six car EMU in advance of intermediate signal 2160 failed at Pomare. In accordance with the rules the six-car EMU in rear passed the Stop & Proceed signal at stop (permission from Train Control not required) and coupled up to the failed train. The twelve car set then ran to Trentham as one train. An unusual working as Ganz EMUs are usually restricted to eight cars maximum.


Stop and Proceed signal



Definition Of Permissive Working.

I wrote this page over nine years ago. Reviewing it in 2013 I realise that the explanations are confusing, maybe even wrong. I am currently upgrading this page.

The problem is probably one of definitions. As I see it now there are three definitions of permissive working. Definition 1 applies to the New Zealand system in 2013.

Definition 1

A train can pass a signal at Stop without the permission of the signalman.

Under this definition a low-speed move onto an occupied track is not permissive working because the signalman has authorised the move and a low-speed light is a proceed indication.

The following definitions are given in the Automatic Signalling Rules introduced north and east of Te Rapa in 2012:

Absolute Signals. A signal that must not be passes at "Stop" without the authority of Train Control or the Signaller as provided for in these rules. Absolute signals are Stop and Stay signals.

Permissive Signals. A signal that is normally controlled by the passage of rail traffic and may be passed without the authority of a Train Controller or Signaller as provided for in these safe working rules. Permissive Signals are Stop and Proceed signals or Stop and Stay signals with "A" lights illuminated.

A quick search of the rules applicable to lines south of Te Rapa in 2013 did not find the word "permissive".

Definition 2

A second train is authorised, either verbally or by signal indication, to enter an occupied section.

Under this definition the use of low-speed lights is a form of permissive working.

Although British practice is not relevant to NZ the followig definition from The Railway Encyclopaedia (EF Carter 1962) is useful:

Permissive Block. The block system by which freight trains are admitted to a line or section of line without the necessity of the previous train having been "cleared". The driver proceeds with caution prepared to stop, until the train in front is reached.

Definition 3

In Single Line Automatic (SLA) signalling the single line section is equipped with an intermediate signal and a second train can follow on signal indications. Known as Absolute Permissive Block (APB). Absolute for opposing trains but Permissive for following trains.

This differs significantly from definition 2 because the second train enters a clear section on signal indications. The train is authorised to travel at Normal speed.





Permissive Working Examples

This section needs to be upgraded or even deleted.

In Automatic Signalling territory there are two basic ways of authorising permissive working - either with a low-speed light or with a Stop & Proceed signal. There are then further combinations depending on whether or not the signal is equipped with an A-Light, is controlled by a signalman or is approach cleared.

It is possible that passing an illuminated low-speed light is not permissive working (because a train is not required to stop). I have included it on this page because the low-speed light merely indicates that any points are set and locked, not that the track is clear.

Here are some examples of permissive working on the New Zealand system.


Train B After a track BT has been occupied for x seconds the low-speed light on approach cleared A2R will illuminate.

Train C The A-light on 10R is illuminated, converting the signal to Stop & Proceed. If the switchlock door is opened 10R goes to Stop and the A-light is turned off, converting the signal to Stop & Ptay. 10R is not controlled by the signalman.

Train D 1975 is an intermediate automatic Stop & Proceed signal - the marker is offset to the right.

Train E 6R is a Stop & Ptay signal controlled by the signalman. The A-Light is illuminated, indicating that the station is switched out and Stop & Proceed rules apply to the signal.

Train F 2R is a Stop & Ptay signal controlled by the signalmen. It is not fitted with an A-Light so the station cannot be switched out. The signalman has turned on the low-speed light.

Train G 2567 is an automatic signal configured as a Stop & Ptay. It can be passed at Stop only on the verbal instructions of Train Control. I am not sure if this is classed as permissive working.




Signal Imperfectly Displayed

In early 2004 I observed permissive working with an interesting variation.


I was on an EMU from Upper Hutt to Wellington. We departed Pomare Station slowly and came to a stop. After a short delay we set off at low speed. This had all the hallmarks of a signal stop so I kept a lookout.

As we passed the double unit Stop and Stay signal Taita 134 Down Home I noticed that the upper unit was Red (as expected, because the front of the train had passed the signal) but that the lower unit was dark. This was a Signal Imperfectly Displayed which is why we had stopped.

Rule 60 (b) in the 1988 Rule Book states:

(b) After stopping at an imperfectly displayed signal a train may proceed only in accordance with the relative Operating instructions applying to the passing of the signal concerned at Stop.

It was the off-peak, Taita Box was switched out and the A-Light was illuminated. This converted the signal to a Stop and Proceed and so we had passed it at Stop in accordance with the rules.

If the A-Light had been off it would have been necessary for the driver to obtain permission from the Taita Signalman to pass the signal - even if the upper unit had been displaying Green.




The Rules

The rules for passing a Stop & Proceed signal at Stop are more complicated than for those for passing a signal with an illuminated Low-Speed light.


Permissive Working With Stop & Proceed Signal

From Double Line Automatic Signalling Regulation 3 (1988 Rule Book):

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 in 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 or handsignalled 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 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.

Permissive Working With Low-Speed Light

Note that this may or may not be permissive working - it depends on which definition is used.


From Rule 58 (1988 Rule Book):

Proceed at low speed, prepared to find track occupied, and ready to stop clear of any obstruction.

Points are in the proper position but track may be occupied, or suitable for low speed only.



Comments

In some parts of the New Zealand Network, eg the Wellington suburban area, an illuminated A-Light may be taken as proof that the points are set and locked. If the signal is displaying Stop, is not protecting a switchlock and the A-Light is not illuminated, the LE must find out if the signal box controlling that signal is switched out. He must have the permission of Train Control to pass the signal. He must stop his train and hand wind the points to check that they are correctly set and secure.

If a low speed light is illuminated any level crossing alarms work correctly, unlike passing a Stop and Proceed signal at Stop. In the latter case the alarms may not work correctly.<



Last Updated: Sun May 19 2013

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