Signalling

Like most signalling systems in the world, New Zealand signalling is based on speed signalling, where the aspect of a signal tells the driver what speed to proceed at. Other different types of rules, such as Centralised Train Control (CTC) and Automatic Signalling Rules (ASR) define how signals work and how they are interpreted. This page mostly deals with ASR as used in the Auckland suburban network between Papakura and Swanson, but most information can also be applied to other signalling rules (albeit with some slightly different terminology).

Please note that none of the information below applies to Track Warrant Control (TWC) areas, as this system uses points indicators rather than signals. Points indicators do not convey authority to proceed and as such are not covered here.

Signal aspects

The simplest signals can display three aspects: green (top), yellow (middle) and red (bottom). Some signals can also display a fourth aspect, flashing yellow (also in the middle). Signals with two heads can display a wider variety of aspects, each of which are explained below. Aspects are typically described by the colour of the top head followed by the colour of the bottom head, e.g. Green over Red for Clear, Normal Speed.

Note: signal aspects not displayed in this table (such as Green over Green) are not valid. Signals displaying an invalid aspect are to be treated as Stop.

Aspect Meaning Common usage
Green Clear
The track is clear ahead, train may proceed at normal speed
Used when the line is clear ahead and the train may travel at the line's, or rolling stock's, speed limit
Flashing Yellow Advance Caution
The next signal is at Caution: prepare to stop at signal after next
Advance warning of a signal displaying Stop; the next signal is displaying Caution
Yellow Caution
The next signal is at Stop
Warning of a signal displaying Stop. Can also indicate the next section of track is clear until the end of the line or an All Trains Stop board.
Red Stop
The train must not proceed
Used when another train is in the section ahead, or the points are not set for the train. May be passed in some circumstances; see Signal types
Green over Red Clear, Normal Speed
The track is clear ahead, train may proceed at normal speed
Used when the line is clear ahead and the train may travel at the line's, or rolling stock's, speed limit
Flashing Yellow over Red Advance Caution, Normal Speed
The next signal is at Caution, Normal Speed: prepare to stop at signal after next
Gives the driver plenty of warning of an upcoming signal at Stop; the next signal is displaying Caution, Normal Speed
Yellow over Red Caution, Normal Speed
The next signal is at Stop
Warning of a signal displaying Stop. Can also indicate the next section of track is clear until the end of the line or an All Trains Stop board.
Red over Red Stop
The train must not proceed
Used when another train is in the section ahead, or the points are not set for the train. May be passed in some circumstances; see Signal types
Red over Green Clear, Medium Speed
The track is clear ahead but is suitable for medium speed only
Often used when the train is switching tracks or taking a diverging route
Red over Yellow Caution, Medium Speed
The next signal is at Stop, and track ahead is suitable for medium speed only
Not often seen, but can be seen when the train switches tracks or takes a diverging route then must stop at the next signal
Flashing Yellow over Green Advance Caution, Normal Speed
Proceed at normal speed, prepare to reduce to medium speed at signal after next
Seen when the train will switch tracks or diverge at the signal after the next one (which is set to medium speed), and the track until then is suitable for normal speed.
Yellow over Green Caution, Normal Speed
Proceed at normal speed, prepare to reduce to medium speed at next signal
Seen when the train will switch tracks or diverge at the next signal (which is set to medium speed), and the track until then is suitable for normal speed.

Speeds

By default, normal speed is the usual line speed, medium speed is 25km/h and low speed is 25km/h. Normal and medium speeds may be changed either by speed boards placed next to the railway, or with speed indicators.

Subsidiary lights

Signals may have any one of these subsidiary lights.

Light Name Description Uses
A capital "A" in a white circle on a black triangle "A" light When lit, converts a Stop and Stay signal into a Stop and Proceed signal "A" lights are lit when a signal box is switched out - it indicates the points are correctly set for either the mainline, loop or branch, but does not guarantee the track is clear. It is also lit if the axle counters fail and have lost track of trains (the next train through resets the signals, a "sweep"), and can also be used to facilitate train rescues in the event of a breakdown or a train is otherwise disabled.
Yellow circle on a white triangle with yellow border Low speed light When lit trains may pass at a maximum speed of 25km/h

Within station limits, low speed lights have similar uses as the "A" light, i.e. they can be used for train rescues or to reset axle counters after failure. The points are in the correct position when this light is lit, but the track may be occupied.

At Britomart Transport Centre and Wellington Station, low speed lights are used to signal trains onto platforms that are already occupied, perhaps because two trains need to couple or all platforms are already occupied, and the incoming train must get in.

On the Johnsonville Branch, low speed lights are used to signal trains onto an opposing main (for example, a Down train onto the Up Main at Khandallah) whether or not the track is occupied. Such use is specific to this line.

Yellow circle on an orange square with white border Restricted speed light When lit trains may pass at a maximum speed of 40km/h Same uses as the low speed light, but is found on departure signals instead
Loop light Points are set for loop or diverging route Used on signals at the start of Track Warrant Control zones - when lit, the points are set for the loop at stations, or the diverging route at junctions
Capital "E" on a white circle Electrified light When lit, the set route is electrified Found on signals which can direct to both electrified and non-electrified tracks; examples are at Papakura and Waikanae. If a signal has this light fitted but not lit, electric trains must not pass the signal even if it otherwise allows trains through (i.e. not at Stop). May be found with any other subsidary lights.
Red circle on black circle Marker light Permanent red aspect Used instead of a marker on single head signals (see below) in dark areas, such as Britomart Tunnel. Can also be used above a signal head to indicate a permanent medium speed aspect - ordinary marker plates are not used above signal heads.

Signal types

Signals generally come in three different classifications: Stop and Stay, Stop and Proceed, and Departure. The classifications relate to the procedures used when passing a signal at Stop. Note that, unlike a car, a train may pass a red signal as long as the driver is following the appropriate rules.

Signals can also come in single-head and double-head varieties. The following table explains the difference between signals.

Single head arrangement Double head arrangement Classification Identifying features Passing at Stop Typical uses
Single head with marker directly underneath Double head with bottom head directly underneath Absolute
Stop and Stay
Red marker or second head directly underneath top head Verbal authorisation by Train Control Almost anywhere - used as directing signals (with a Low Speed light) as well as intermediate signals (with an "A" light). Double head signals are almost always found controlling turnouts, and indicate the permitted speed for the set route.
Single head with marker below and to the right Double head with bottom head below and to the right Permissive
Stop and Proceed
Red marker or second head below and to the right of top head Train must stop for 10 seconds, then the driver may proceed at such a speed that they can stop in half the visible distance Single head permissive signals are used on double line block sections (outside bi-directional areas) as intermediate signals, allowing greater capacity than with absolute signals alone. In Auckland, double head permissive signals are used on the opposing main (e.g. for a Down train running on the Up Main) as an advance warning of the upcoming absolute signal at the end of the block section.
Single head with marker directly underneath and blue Depart board Double head with marker directly underneath and blue Depart board Departure Like absolute, with blue Depart sign on signal number plate A SWA1 (Auckland, ASR) or Mis. 59 (elsewhere) form must be issued Authorises entry into a block section from interlocked stations

Route and speed indicators

Some signals may have a route indicator, speed indicator or both. Route indicators are typically found below the signal heads and tell the driver which route the train is taking, shown with one or two characters. The meaning of the characters is specific to each signal, but usually follows conventions such as "D" for Down Main.

PAP 2220 signal with route indicator below signal heads
Signal PAP 2220, with the route indicator at the bottom showing "U" for Up Main. This particular route indicator only shows this and "D" for Down Main, but others can display many more indications than this, usually with two letters such as "D1" (Down Main on the NAL) on signal WSF 1504

Speed indicators are usually above the signal heads, and indicate to the driver the speed they may travel at when a signal is set to any aspect other than Clear or Stop.

Unusual signals

Of course where there are rules, there are exceptions! Some signals aren't quite the same as others.

Photo Signal identification Features
PAP 2231 Papakura Up Main (northbound track) signal for southbound trains - signal is permanently at Stop as this marks the end of ASR and bi-directional signalling
MNK 1904 signal head MNK 1904 Manukau Platform 2 departure - upper signal head has no green light as Clear, Normal Speed is not possible, as two signals ahead is the junction with the North Island Main Trunk, suitable for medium speed only. The lack of a lens is visible in the large version of the photo to the left (click to enlarge).
AKD 127 signal with route indicator above signal heads AKD 127, AKD 129, AKD 34, AKD 36 Auckland inbound from Orakei (opposite port sidings) Up and Down Mains, Auckland outbound (near Vector Arena footbridge) Up and Down Mains - route indicators above the signals heads due to clearance issues

Changelog

  • 20 October 2014: Add brief reference to Track Warrant Control, fixed image
  • 11 February 2014: Removed references to intermediate speed aspects
  • 23 January 2014: Improved mobile version, fix a light image
  • 20 January 2014: Launch signalling page

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