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The signal box provided a dry, climate-controlled space for the complex interlocking mechanics and also the signalman. The raised design of most signal boxes (which gave rise to the term "tower" in North America) also provided the signalman with a good view of the railway under his control. The first use of a signal box was by the London ...
An example is the process of signalling a train in the up direction (from A to C) past a signal box B. The signal box in rear is A and the signal box in advance is C. [2] The block indicators at B are in the Normal position. The signalman at A "offers" the train to B by sending an "Is Line Clear?"
In the simplest case with three signal boxes on a stretch of line without junctions, the central of the three boxes will receive a request for a train to be accepted, the signaller will set any relevant points (turnouts) and signals and signal acceptance, and then request acceptance by the next signal box along the line.
The tuned circuit often incorporates the circuit to either apply the transmitted signal to the track or recover the received signal from the other end of the section. Consider a railway with two block sections as in the diagram. Section 1 has frequency A injected at the left-hand end and received at the right-hand end.
A mechanical lever frame inside the signal box at Knockcroghery in Ireland Waterloo station A signalbox, LSWR (Howden, Boys' Book of Locomotives, 1907). Mechanical railway signalling installations rely on lever frames for their operation to interlock the signals, track locks [1] and points to allow the safe operation of trains in the area the signals control.
For example, interlocking would prevent a signal from being changed to indicate a diverging route, unless the corresponding points/switches had been changed first. In North America, the official railroad definition of interlocking is: " An arrangement of signals and signal appliances so interconnected that their movements must succeed each ...
Examples of single line tokens: Tablet on left, key token on right. The operation of a bidirectional single track line has the hazard of two trains colliding. The simplest way to prevent such collisions is to have only one train in the section at any given time. Such a system is known as "one-engine-in-steam” (OES) or “one-train working ...
The first reached by a train is known as the home signal. The last stop signal, known as the starting or section signal, is usually located past the points etc. and controls entry to the block section ahead. The distance between the home and starting signals is usually quite short (typically a few hundred yards), and allows a train to wait for ...