NZR Signals

Introduction

Signalling of trains became a must very soon after their acceptance as a viable means of transport. All early developments were in Britain where a host of different systems were developed, some surviving and developed further into more modern signally systems, some only used on an individual line and soon replaced by what were seen as better systems. The need for signals was of course an attempt to prevent the spate of horrific accidents that occurred, and as no system eliminated all types of accidents, the things that were learned from each subsequent accident, helped define new goals for the systems that were in use.

There are several aspects to a signalling system, the physical signals can indicate to a train driver that he has permission to proceed. In the early days of railways that was all that was provided and the driver could assume that there was no other train on the track. Where a train's route was long, signals could be positioned at locations along that route to keep trains at a safe distance from the train ahead.

As the railway became more complex, particularly with regard to station yards, the signalling system also had to ensure that the way was safe for the train to travel through the many sets of points. This meant a physical connection was required between those points (turnouts) and the signal box, so the signalman could set a safe route. Such a system was called interlocked, in that, provided the signalman had done his job properly, it 'locked' the route for the expected train.

All early signalling systems required a signalman to control the individual signals and the set of points that it was usually associated with. At stations there were often too many signals for one signal man to work because they were not always close together, and so the concept of the signal box evolved, where one signal man could control many signals. They was a physical connection between a lever in the signal box and a signal or the movable points of a turnout. The signals were usually connected by a wire cable, and the points bt steel rods, and referred to as rodding. For very big yards, two or even three signal boxes were were required to keep the distance to furthest point to be controlled to a manageable distance.

Signals are the interface between the tracks that trains run on and the drivers of those trains. As such they need to operate in a reliable way and all systems that are installed are therefore subject to regular testing to ensure the meet required standards. Many systems are very complex, and therefore systems have been standardised to behave in predictable ways. A driver can then confidently operate his train on completely different sections if they both have the same signalling system. There is a further interface between the signalling system and the driver, and that is known as the Signalling and Interlocking Circular (or Diagram) or S&I circular for short. These documents record the tracks and signals on the various section of a railway and their relative positions, and the driver then knows what to look out for. These diagrams have been produced since the first signalling systems were installed

The New Zealand Scene

New Zealand was in some ways in a fortunate position, as the introduction of railways here was still a good number of years behind developments in Britain. This both allowed us to learn from some of the early mistakes made there, and also be in a position to purchase ready made solutions to the challenges that were faced in the world of railway signalling.