The three position signal system signals by three positions (horizontal, 45 degrees, and vertical) of the arm of semaphore signal and a set lights of position light signal, and also by red, orange, and green of the color light signal.
The color light signal displaying three kinds of signals (stop signal, warning signal, and proceed signal) is called "three signalings of three position signal", and displaying four kinds of signals ( stop signal, warning signal, deceleration signal, and proceed signal) is called "four signalings of three position signal", not "four position signal".
Another rough classification of the signaling system is "route display signal" and "speed display signal", according to the difference in displaying contents to indicate train operation.
The route display signal indicates operation do's and don'ts according to each route, such as from what line, which route, until where, and how (speed, etc.) the train may operate.
Such operating conditions as maximum speed are accordingly up to the conductor.
Speed display signal indicates only the speed to maintain at the present, such as at what speed the train may proceed, based on route conditions.
Cab signals adopted for Shinkansen and commuter train sections in and near Tokyo operate by this system.
(2) Fixed signal
Fixed signals classified as main signal, subsidiary signal, and signal appendages are fixed on the ground to display signals.
a. Main signal
Main signals protect a section by signaling (signaling ensuring safety of a certain section). Among the main signals, home signal and departure signal are called "absolute signals" which do not allow non-block operation. The blocking signal is called the "permissive signal", because it permits non-block operation. Since they are distinguished in train operation, the identification marker is attended on blocking signals.
Applications of main signals are as follows.
Home signal : Signal for trains entering the station
Departure signal : Signal for trains departing the station
Blocking signal : Signal for trains entering the block section
