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A position light signal is one where the position of the lights, rather than their colour, determines the meaning. The aspect consists solely of a pattern of illuminated lights, which are all of the same colour. In many countries, small position light signals are used as shunting signals, while the main signals are of colour light form.
There are two main types of signaling aspect systems found in North America, speed signaling and weak route signaling. [citation needed] Speed signaling transmits information regarding how fast the train is permitted to be going in the upcoming segment of track; weak route signaling transmits information related to the route a train will be taking through a junction, and it is incumbent upon ...
Position light signal (Pennsylvania) Signals made by the Pennsylvania Railroad that make use of a circular disc with up to eight lights mounted in a circle, with one light in the center. The lights would line up in a straight line to give the indication. [194] [195] Power Move (PM)
A Class 66 locomotive (right) is waiting at a red signal while a First Great Western (now Great Western Railway) passenger train (left) crosses its path at a junction. Railway signalling (BE), or railroad signaling (AE), is a system used to control the movement of railway traffic.
"Wigwag" was the nickname given to a type of crossing signals once common in North America, named for the pendulum-like motion it used to signal the approach of a train. Albert Hunt , a mechanical engineer at Southern California 's Pacific Electric (PE) interurban streetcar railroad, invented it in 1909 for safer railroad level crossings.
Track circuits allow railway signalling systems to operate semi-automatically, by displaying signals for trains to slow or stop in the presence of occupied track ahead of them. They help prevent dispatchers and operators from causing accidents, both by informing them of track occupancy and by preventing signals from displaying unsafe indications.
Electric color light signals require replacement of failed bulbs, and checking of electric circuits and relays, and replacement of failed electrical components. [18] Signal maintaining staff would also assist in the care and upkeep of railroad switches, such as removal of debris preventing switches from moving, oil and greasing of motors.
The signal was turned off if the block were not "clear"; no current passed through the coherer and a relay turned a white or green light in the cab to red and applied the brakes. [5] The London & South Western Railway installed the system on its Hampton Court branch line in 1911, but shortly after removed it when the line was electrified. [6]