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Double junction, or level junction (left hand running). A double junction is a railway junction where a double-track railway splits into two double track lines. Usually, one line is the main line and carries traffic through the junction at normal speed, while the other track is a branch line that carries traffic through the junction at reduced speed.
If the overlap is long enough to extend from one stop signal to the next, then the effect is to provide two signal protection (or "double blocking"), with the first signal having a full overlap, and the second signal having a short overlap. With two signal protection, only one track circuit is needed between successive signals. However ...
There are two main types of signaling aspect systems found in North America, speed signaling and weak route signaling. [citation needed] Speed signaling transmits information regarding how fast the train is permitted to be going in the upcoming segment of track; weak route signaling transmits information related to the route a train will be taking through a junction, and it is incumbent upon ...
When the junction signal is not at danger, both heads show an aspect: the one for the route set ahead of the junction (left or right) shows the correct aspect while the other shows single yellow (or double yellow at an "outer splitting distant").
In any given country, rail traffic generally runs to one side of a double-track line, not always the same side as road traffic. Thus in Belgium, China, France (apart from the classic lines of the former German Alsace and Lorraine), Sweden (apart from Malmö and further south), Switzerland, Italy and Portugal for example, the railways use left-hand running, while the roads use right-hand running.
Most blocks are "fixed", i.e. they include the section of track between two fixed points. On timetable, train order, and token-based systems, blocks usually start and end at selected stations. On signalling-based systems, blocks start and end at signals. The lengths of blocks are designed to allow trains to operate as frequently as necessary.
Automatic block signaling (ABS), spelled automatic block signalling or called track circuit block (TCB [1]) in the UK, is a railroad communications system that consists of a series of signals that divide a railway line into a series of sections, called blocks. The system controls the movement of trains between the blocks using automatic signals.
A junction, in the context of rail transport, is a place at which two or more rail routes converge or diverge. The physical connection between the tracks of the two routes (assuming they are of the same gauge) is provided by turnouts (US: switches ) and signalling .