Signalling Principles

This page explains the principles of New Zealand signalling and safeworking. The emphasis is on automatic signalling and the Hutt Valley Line.

Right The Johnsonville Branch Up Departure signal. The All Trains Stop board was installed after a wrong side failure with a tri-colour signal head in Australia (Jan 2008). Special procedures apply to passing this signal. The smudge is on the EMU front window, not the camera lens!

Home  > Signalling Principles  

Overview   Signal Aspects   Classification   Overlaps   Subsidiary Lights   Loop Exit   Permissive   Examples   Wellington Junction Signalling   Wellington Diagram   Points Indicators   Trap Point Mechanisms   Safe Working   19th Century Signalling in 2004   History   South Junction   Johnsonville   Boards   Colour Light Shunt Signals   Comparative Aspects  

Overview

The safe operation of a railway depends on the signalling (i.e. the hardware) and the operating rules that define how the hardware is to be used (i.e. the software). The two are separate - there could be more than one set of rules applying to a particular set of hardware. In practice, there is a one to one relationship between the signalling and operating rules. My Signalling Overview page decribes the situation in New Zealand.

Signal Aspects

Signal aspects are explained in New Zealand Signal Aspects and also the NZR training document Illustrated Guide To Three Position Colour Light signals. This booklet dates from the 1960s or 1970s and does not describe two newer aspects - Advance Caution and Intermediate Speed.

My Medium Speed page uses a diagram and a sequence of photographs to explain medium speed. The location is Trentham and I also show how the meaning of a signal can be changed by a speed board.

Read about the differences between Two-Position and Three Position signalling.

Classification

The signal classification determines the rules that apply when a signal is to be passed at stop.

Overlaps

A set of six photographs demonstrate overlaps on the Hutt Valley Line.

Subsidiary Lights

• My Subsidiary Lights page describes the subsidiary lights used or proposed for use on the New Zealand railway system.
  
• Diagrams and photographs explain A-Lights.
• A set of three photographs show a low speed light signalling a train onto an occupied track at Wellington Station.
• A diagram and photographs explain signal markers. At Maymorn a full size searchlight unit is used as a marker light - see my Large Signal Marker Light page.

Loop Exit

The railway in New Zealand has used various signal configurations for controlling the exit of a train from a loop - ground lights, single unit running signals and double unit running signals. My Loop Exit page uses diagrams and photographs to document examples between Ngauranga and Featherston.

Permissive Working

In Double Line Automatic territory there are various situations in which permissive working is authorised.

In southerly conditions the section through Ngauranga sometimes requires permissive working. Sea water on the tracks drops the track circuits putting the signals to Stop. This is demonstrated in these driver's photographs.

Ngauranga To Wellington

The Ngauranga to Wellington section provides a variety of examples of New Zealand double line automatic signalling practice, including:

• Advance Caution Indication.
• Two methods of permissive working.
• Approach cleared Low-Speed lights allow trains to stack up without the intervention of the signalman.
• Train Stops.
• A-Lights
• Switch out station.
• Searchlight and three lens signals.

Wellington Junction Signalling

New Zealand railways use speed signalling. However there are locations where the signalling indicates the route and speed boards define the authorised speed. One example is Up trains at Wellington Junction. In contrast Down trains at Wellington Junction are directed with signals that more closely follow speed signalling conventions. On both of these pages I use a diagram and some photographs to show how notice boards can change the meaning of a signalling installation.

Wellington Station Layout

I have scanned a 1937 diagram of Wellington Station in two parts. The north end shows the original junction layout. The south end shows the platform names and the dotted in tenth platform.

Mechanical Points Indicators

A diagram and photographs explain the rules applying to mechanical points indicators.

Trap Point Operating Mechanisms

Trap points and safety points protect the mainline and loops from runaway vehicles. I have created a series of pages which use diagrams and photographs to explain the mechanisms used to operate these points.

To learn how the horizontal motion of a rod can be converted into three separate actions - unlock the facing point lock (FPL), throw the switch, lock the the FPL, visit my Economical FPL page.

There are six trap points extant between Woburn and Trentham. In addition there is a set of safety points at Upper Hutt and other turnouts at Upper Hutt and Woburn which perform the same functions as safety points. I have documented these structures on my Mainline Protection page. The main page summarises the structures and provides links to a detail page for each structure. The detail pages use a diagram and photographs to explain the operating mechanism of each set of points. What makes the trap and safety points so interesting is the differences between installations. Items which can differ include:

• Mechanism operated by motor, lever or rodding.
• Rodding fitted with temperature compensator.
• Switches detected electrically.
• Switches individually detected or combined with a scalebeam.
• Switches fitted with a facing point lock.
• Switches fitted with an "Economical" facing point lock.
• Traps protected with colour light or points indicator.
• Mechanism located next to points or some distance away.

Safe Working

My Safe Working page provides links to html and pdf versions of the following safe working documents:

• 1943 Regulations for Working Single Line Railways by the Train Staff And Ticket System.
• 1965 Regulations for Working Single Line Railways by the Electric Train Tablet System.
• 1965 Regulations for Automatic signalling.
• Generic Track Warrant Control Regulations.
• 1965 Rules

19th Century Signalling

In 2004 at Masterton some interesting relics of late 19th/early 20th century signalling are still in regular use on the commercial railway. Masterton is the only location I know of where a Woods key is still used and is one of only two or three stations that have two-position signals.

Hutt Valley Signalling History

My Hutt Valley Signalling History page documents the history of signalling in the Hutt Valley and also on the Rimutaka tunnel route to Featherston.

South Junction Temporary Signalling

In March 2002 a low-speed light was installed on the Up Departure signal at Pukerua Bay. The purpose was to allow Up EMUs to reverse on the single line during a Block Of Line. The line was closed between South Junction and Waikanae for tunnel floor lowering and other work.

Pukerua Bay is on the North Island Main Trunk Line (NIMT), not the Hutt Valley Line. However the signalling work was so interesting that I have included it on my site. Visit my South Junction Temporary Signalling page for details of this work. The page also explains signal classes, Mis 59 forms, low-speed lights and the normal South Junction signalling.

Johnsonville Line

The Wellington - Johnsonville Line is now controlled by CTC but has had some interesting features over the years. Although it is not in the Hutt Valley I have created a Johnsonville Line Signalling page. Some of the interesting features include:

• Stop on Green & proceed on Yellow to reduce delays.
• Low-Speed lights prove track clear.
• Starting signals at Ngaio and Khandallah to allow trains to be divided.
• Mechanical signalling at Thorndon, Ngaio and Johnsonville.
• Speed control with train stops.

Boards

A variety of boards are seen by drivers as they go about their daily work.

Colour Light Shunt Signals

Although the same set of rules applies to every shunt signal, the way in which individual shunt signals operate can differ. I explain the rules applying to shunt signals and then, using Petone as an example, explain some of the ways in which their operation can differ.

Comparative Aspects

My Comparative Aspects page compares the aspects used in New Zealand with those used by the Rail Infrastructure Corporation (RIC) in NSW and the Burlington Northern and Santa Fe (BNSF). The comparison is not a comprehensive explanation of RIC or BNSF signalling. The purpose of the page is to demonstrate that there are many different ways of defining colour light signal aspects.