The signal system is a general term for signal devices which indicate train operating conditions to train conductors; blocking devices to ensure safe train operation, interlocking devices, level crossing safety devices, etc.
At first, trains in Japan were operated without blocking or interlocking devices. Instead, the telegraph was used for arrangements, and signals were manually displayed according to the time schedule.
Later, due to the growing number of trains passing each other in transit, separate personnel became necessary for switching points, displaying signals and communication. This led to the development of "interlocking devices" to link mechanized signals and switch points.
The greater number of trains also increased the danger of train collisions. "Blocking devices" were developed to prevent collisions by permitting only one train to run in established block sections.
At the same time, electric equipment for railways made remarkable progress. This facilitated the linking of signal, blocking, and interlocking devices, etc., resulting in steady advances in the signal safety system.
Nevertheless, accidents due to human error will be difficult to reduce so long as train operation is based on human attentiveness, since it is the driver who actually operates the train. Even if signal devices and cars are modernized, they will not help reduce human error accidents unless both are linked.
It is for this reason that ATS was developed. ATC also links train speed control and signal display.
The signal system in stations has also been modemized. The introduction of the relay interlocking device electronically interlocks point levers and others by electromagnetic relays.
This has made possible total route control at the station by small levers and buttons on the control panel, instead of points being switched at each switch point as before.
CTC gives train dispatchers control all signals and switch points in the stations in the CTC zone by remote control system and dispatchers control traffic swiftly and properly with the display of train locations on the display panel.
The division between the roles of people and machines in train operation is changing and facilities are becoming more complex with the advancing modemization of various facilities.
