Facing and trailing
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Facing and trailing are terms used to describe railway turnouts (or 'points' in the UK) in respect to whether they are divergent or convergent. When a train traverses a turnout in a facing direction, it may diverge onto either of the two routes. When travelled in a trailing direction, the two routes converge onto each other.
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[edit] History
In the early history of railways in Britain, when signalling and interlockings were primitive, and staff were inexperienced, facing turnouts were a hazard, because they could switch a train travelling at high speed into a slow speed divergence or dead end. Facing turnouts were therefore banned, except when absolutely necessary. Facing turnouts cannot be avoided on single lines and their crossing loops.
[edit] Diamond crossings
Fixed diamond crossings (with no moving parts) count as trailing points in both directions, although in very exceptional circumstances such as propelling a train in reverse they can derail wagons as they bunch up.
So-called switch(ed) diamonds, which contain two stub turnouts in disguise, count as facing turnouts in both directions and are also known as moveable angles (UK).
[edit] Recent times
With the widespread availability of electrically interlocked signalling in modern times, the rule against facing turnouts has been relaxed.
[edit] Double junctions
Double junctions are now configurable in a number of different ways, whereby the number of facing and trailing turnouts vary.
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