Breather switch

Expansion joint on Williamsburg Bridge, New York City Subway

A breather switch on a TGV line

A breather switch, expansion joint, or adjustment switch is an intentional gap in railway tracks to allow for expansion in long sections of otherwise unbroken rail. They are placed between very long sections of continuous welded rail (CWR) or at the transition between CWR and jointed track, and commonly in the vicinity of bridges and viaducts where the infrastructure and track may expand at different rates.

The mating sections are tapered diagonally (unlike a butt joint 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 trains, and, where CWR is particularly prone to expansion, they act as relief points to ensure that track does not warp out of shape or cause a sun kink.

References

Railway infrastructure
Permanent way	Permanent way (history) Permanent way (current) Railroad tie/Sleeper Rail fastening system Track ballast Rail profile Fishplate Breather switch Datenail Axe ties Ladder track Baulk road Cant Minimum radius Track transition curve Clip and scotch
Trackwork and track structures	Junction Wye Railroad switch Gauntlet track Railway electrification system Third rail Overhead lines Guide bar Track gauge Track geometry Railway turntable Water crane Track pan Coaling tower Rail track Tramway track Classification yard Rail yard Siding Passing loop Balloon loop Headshunt Refuge siding Dual gauge Roll way
Signalling and safety	Derail Railway signalling Signalling control Wayside horn Railway signal Interlocking Level crossing Buffer stop Catch points Loading gauge Structure gauge Block post Train stop Signal bridge Tell-tale
Buildings	Railway station Station building Railway station layout Station clock Train shed Goods shed Motive power depot Roundhouse Railway platform

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