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Railway Stage Signaling

There're two main kinds of block systems on stages.

Automatic block system

Automatic block systems is widely used on railways because it significantly increases throughput of the stage in comparison with semi-automatic block system.

The stage is divided into several block sections that have length from 1000 m up to 2700 m. There are wayside automatic signals between block sections that allow the train to enter the next block section if it's free. The system checks whether the next block section is free automatically using track circuits.

Automatic block system
Wayside automatic signal

Automatic block system is multi-aspect signaling. Three-aspect signaling is used in most of cases.

  • Green light allows to go. There are two or more free block sections.
  • Yellow light allows to go. There is just one free block section. Be ready to stop by the next wayside automatic signal.
  • Red light requires stopping.

On railway lines close to large cities where suburban traffic is rather heavy four-aspect signaling is used.

  • Green light allows to go. There are three or more free block sections.
  • Green and yellow lights together allow to go. There are two free block sections.
  • Yellow light allows to go. There is just one free block section. Be ready to stop by the next wayside automatic signal.
  • Red light requires stopping.

permissive signal

On stages with long ascending grades sometimes it's allowed for heavy freight trains to keep going not faster then 20 km/h if wayside automatic signal is red. There's a table with a letter "T" (from the Russian word "heavy") on such a signals.

Not letters, but numbers assigned to name wayside automatic signals. The numbers are odd in the odd direction and even in the even direction. The numbers are put in descending order.

Pre-home signal

Wayside automatic signals that are neighboors to station home signals are called "pre-home" always have numbers 1 (odd) and 2 (even) and have special table on them.

Cab signaling (ALSN - automatic locomotive signalling of continuos action) is always used in combination with automatic block system.

Semi-automatic block system

The stage equipped with semi-automatic block system usually don't have track circuits. Just one train can be on the stage between two stations on one track.

Semiautolocking
Precautionary signal

To depart train station duty officer should receive special blocking signal from the neighboor station duty officer.

When the train arrives station duty officer should ensure that the stage is free (no cars of the train have left there) and press special button to send arrival signal to the neighboor station. Then the stage is considered to be free.

On stages equipped with semi-automatic locking there's just one precautionary light signal before the next station's home signal. The distance from precautionary signal to home signal should be more than braking distance of the train. Usually the distance is 1-3 km. If there's a yellow light on it train engineer should be ready to stop before home signal with a red light.

The main rule of semi-automatic block system is that there should be just one train per one stage track.

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