This may be applied for sighting reasons, or simply to extend the life of the lamp and save the batteries. Some types of signal display separate permissive and absolute stop aspects.Īpproach lighting leaves the signal dark (or dimmed) when a train is not present. In US practice a permissive signal typically is indicated by the presence of a number plate. In current British practice for example, automatic signals have a white rectangular plate with a black horizontal line across it. ĭrivers need to be aware of which signals are automatic. those controlled through track occupancy alone, not by a signalman) are usually permissive. Interlocking ('controlled') signals are typically absolute, while automatic signals (i.e. Furthermore, a permissive signal may be marked as a Grade Signal where a train does not need to physically stop for a "Stop & Proceed" signal, but only decelerate to a speed slow enough to stop short of any obstructions. When a train is waiting at a signal it is "in rear of" that signal and the danger being protected by the signal is "in advance of" the train and signal.Ī distinction must be made between absolute signals, which can display a "Stop" (or "Stop and Stay") indication, and permissive signals, which display a "Stop & Proceed" aspect. The term "ahead of" can be confusing, so official UK practice is to use the terms in rear of and in advance of. Signals are sometimes said to "protect" the points/switches, section of track, etc. They may also convey information about the state of the next signal to be encountered. Signals control motion past the point at which the signal stands and into the next section of track. Operating rules normally specify that when there is some imperfection in the display of an aspect (e.g., an extinguished lamp), the indication should be read as the most restrictive indication consistent with what is displayed. The red light in this instance does not indicate "Stop" it is simply a component of a larger aspect. In the United States, for example, it is common to see a "Clear" aspect consisting of a green light above a red light. It is important to understand that for signals that use colored aspects, the color of each individual light is subsumed in the overall pattern. In the background, express train 81 is pulling away from the station. Aspects and indicationsĪ Finnish distant signal at the western approach to Muhos station is displaying Expect Stop. Signals are generally not provided for controlling movements within sidings or yard areas. Where 'bi-directional' signalling is installed, signals face in both directions on both tracks (sometimes known as 'reversible working' where lines are not normally used for bi-directional working). Each line of a double track railway is normally signalled in one direction only, with all signals facing the same direction on either line. 'Running lines' are usually continuously signalled. ahead of platforms or other places that trains are likely to be stopped.on the approach to a movable item of infrastructure, such as points/switches or a swingbridge.that the train orders are to be picked up by the crew.that points (also called switch or turnout in the US) are set correctly.
PRR SEMAPHOR TRAIN SIGNAL RULES DRIVER
Under timetable and train order operation, the signals did not directly convey orders to the train crew. This allowed for an increase in speed, since trains no longer needed to be able to stop within sighting distance of the stop signal. The distant signal gave the driver warning that he was approaching a signal which might require a stop. One such refinement was the addition of distant signals on the approach to stop signals. As traffic density increased, this proved to be too limiting and refinements were added. Originally, signals displayed simple stop/proceed indications. Main article: Application of railway signals
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