A breather switch, expansion joint, or adjustment switch is an intentional gap in

railway track A railway track (British English and UIC terminology) or railroad track (American English), also known as permanent way or simply track, is the structure on a railway or railroad consisting of the rails, fasteners, railroad ties (sleepers, ...

s to allow for thermal expansion in long sections of otherwise unbroken rail. They are placed between very long sections of

continuous welded rail A railway track (British English and UIC terminology) or railroad track (American English), also known as permanent way or simply track, is the structure on a railway or railroad consisting of the rails, fasteners, railroad ties (sleepers ...

(CWR) or at the transition between CWR and jointed track, and commonly in the vicinity of bridges,

viaduct A viaduct is a specific type of bridge that consists of a series of arches, piers or columns supporting a long elevated railway or road. Typically a viaduct connects two points of roughly equal elevation, allowing direct overpass across a wide v ...

s and tunnels where the infrastructure and track may expand at different rates. The mating sections are tapered diagonally (unlike a

butt joint A butt joint is a technique in which two pieces of material are joined by simply placing their ends together without any special shaping. The name "butt joint" comes from the way the material is joined. The butt joint is the simplest joint to ma ...

between two lengths of rail), allowing smoother transitions and higher speeds across the gap. Breather switches have two advantages over jointed track: they greatly reduce the small gap between the rails, eliminating or significantly reducing the noise and vibration caused by passing

train In rail transport, a train (from Old French , from Latin , "to pull, to draw") is a series of connected vehicles that run along a railway track and Passenger train, transport people or Rail freight transport, freight. Trains are typically pul ...

s, and, where CWR is particularly prone to expansion, they act as relief points to ensure that track does not warp out of shape or result in a sun kink.

References

Permanent way {{Rail-transport-stub