Railway signalling in Kulpania

Railway signalling in Kulpania is primarily achieved through the use of lineside signals to control the movement and speed of trains. On most non-high-speed lines operated by KulpanRail, either three- or four-aspect colour-light signals are used, with the additional aspect being used on lines with a higher speed limit to provide additional warning of an upcoming stop signal. On high-speed lines, signalling is instead performed through in-cab signalling, meaning that trains designed for low-speed lines cannot run on lines designed for high-speed trains.

Light-rail and metro systems are not required to use the same signalling system as KulpanRail lines, so many use their own approaches to signalling.

History

The first commercial railway in Kulpania was opened in 1841 between Dalow and Minlesoca, and was dual-track from the beginning. Upon opening, a rudimentary system of signalling was used, wherein only one train could occupy the section of track between two adjacent stations. Namely, once a train had departed Dalow, the next train was not allowed to depart in the same direction until the signaller at Dalow received confirmation from the next station on the line that the train had departed.

This system was copied by other lines opening in the following years. Some lines added signal boxes where the distance between two adjacent stations was too long, where the signal box acted as another point at which a signaller could be stationed to monitor the positions of trains on the line.

This system quickly became insufficient as demand for the railways grew dramatically. The first line to employ a new signalling system was the line between Lowtah and Tondil, opened in 1873 by the Lowtahtor Railway Company. Signalling for this line was instead performed through use of semaphore signals placed at regular intervals, where all the signals from one station to the next were controlled by the signaller at the station which was closer to the Lowtah end of the line. The signaller could monitor the position of the train through a series of bells: as a train passed over certain points on the track, the weight would cause tension in a wire which caused a specific bell to ring in the signaller's office.

As more intercity lines were built, the semaphore-bell signalling system spread. Older lines originally built without signals were gradually upgraded to also employ semaphore-bell signalling. Railway lines continued to be built with this approach to signalling until 1922. With the formation of KulpanRail, the standard was switched so that all lines should have electrical signalling. All subsequent lines were built with electrical signalling as standard, and existing lines were retrofitted with new signals over the next four years.

Current system

The lowest-speed lines use three-aspect signals. From top to bottom, these signals have one red, one yellow, and one green light. The patterns used are as follows:

• Green - Clear. The train may proceed, and the driver may assume that the line ahead is clear for some distance.
• Green and yellow - Warning. The train may proceed, but the next signal is displaying Stop.
• Red - Stop. No train may proceed, unless special permission has been given by the signaller.
• Yellow - Branching. The train may proceed, but will be diverting from the current line before the next signal. These signals are always accompanied by an additional light affixed below which shows an arrow to indicate in which direction the train will be diverting.
• Yellow and red - Fault. The train may proceed at a low speed. The next signal has a fault and should be ignored. This signal is rarely used, even when there is a fault with signals, because it is thought to cause too much confusion. However, all drivers are still trained to recognise it.

Lines designed for higher speeds have an additional yellow aspect. These signals still display all the same patterns as listed above, as well as the following additional patterns:

• Green and double yellow - Pre-warning. The train may proceed, but the next signal is displaying Warning.
• Double yellow - Pre-branching. The train may proceed, but the next signal is displaying Branching.

Repeaters

In some locations, signals have poor visibility. In this case, repeater signals are used to indicate to the driver what the upcoming signal is displaying. They should only be treated as an indicator of what is coming up, and should not be used as the final authority (for example, if a repeater signal is indicating that the next signal is Stop, the driver can still proceed past the repeater).

Repeater signals have the same format as regular signals, but with an additional white light on top which is permanently illuminated. If the white light is not illuminated (which can only happen if there is a fault with the signal), the driver should treat the repeater as a regular signal.