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A Pennsylvania Railroad high signal displaying Approach Medium Amtrak colorized position lights at Trenton, New Jersey. Position light signals use rows of 5 + 3 ⁄ 8-inch-diameter (140 mm) lamps to simulate the positions of an upper quadrant semaphore blade.
The invention of the electric light, which could be made brighter than oil lamps and hence visible both by night and day, resulted in the development of position light signals and colour-light signals at the beginning of the 20th century, [11] which gradually displaced semaphores. [12] A few remain in modern operations in the United Kingdom. [13]
Timetable and train order was not used widely outside North America and has been phased out in favor of radio dispatching on many light-traffic lines and electronic signals on higher-traffic lines. The only railroads currently still using authentic train order operations is the South Shore line in Indiana and the LIRR in New York.
Green: Proceed at line speed. Expect to find next signal displaying green or yellow. Yellow: Prepare to find next signal displaying red. Red: Stop. On some railways, colour light signals display the same set of aspects as shown by the lights on mechanical signals during darkness.
"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.
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)
Some crossings have a sign saying "signal automatique" (automatic signal). French level crossings with more than one track have a sign saying "un train peut en cacher un autre" (a train can hide another train). As of 2016 France has 15,459 level crossings (by comparison, there were 33,500 in 1938 and 25,000 in 1980).
The track circuit can be split with extra blockjoints and the detectors in the points complete the track circuit when the points are normal and the signal is entitled to receive a green light. This is partially fail-safe. A second relay can be installed on the turnout, with its contacts wired in series with the main relay.