Editing Railroad switch (section)

==Design==
The parts of a turnout are known by different names in different jurisdictions. The main terms in U.S. and UK usage are shown in the selectable diagrams. In this article, the U.S. term is listed first and UK second, in parentheses.

The most common type of switch consists of a pair of linked tapering rails, known as ''points'' (''switch rails'' or ''point blades''), lying between the diverging outer rails (the ''stock rails''). These points can be moved laterally into one of two positions to direct a [[train]] coming from the point blades toward the straight path or the diverging path. A train moving from the narrow end toward the point blades (i.e. it will be directed to one of the two paths, depending on the position of the points) is said to be executing a ''facing-point movement''.

For many types of switch, a train coming from either of the converging directions will pass through the switch regardless of the position of the points, as the vehicle's wheels will force the points to move. Passage through a switch in this direction is known as a ''trailing-point movement'' and switches that allow this type of movement without damage to the mechanism are called ''trailable switches''.<ref>{{cite book |title=Railroad Classification Yard Technology Manual |publisher=U.S. Department of Transportation, Federal Railroad Administration, Office of Research and Development |date=1981 |page= }}</ref>{{Page needed|date=April 2025}}

A switch generally has a straight "through" track (such as the main-line) and a diverging route. The handedness of the installation is described by the side that the diverging track leaves. ''Right-hand switches'' have a diverging path to the right of the straight track, when coming from the point blades, and a ''left-handed switch'' has the diverging track leaving to the opposite side. In many cases, such as rail yards, many switches can be found in a short section of track, sometimes with switches going both to the right and left (although it is better to keep these separated as much as feasible). Sometimes a switch merely divides one track into two; at others, it serves as a connection between two or more parallel tracks, allowing a train to ''switch'' between them. In many cases, where a switch is supplied to leave a track, a second is supplied to allow the train to reenter the track some distance down the line; this allows the track to serve as a siding, allowing a train to get off the track to allow traffic to pass (this siding can either be a dedicated short length of track, or formed from a section of a second, continuous, parallel line), and also allows trains coming from either direction to switch between lines; otherwise, the only way for a train coming from the opposite direction to use a switch would be to stop, and reverse through the switch onto the other line, and then continue forwards (or stop, if it is being used as a siding).

A ''straight track'' is not always present; for example, both tracks may curve, one to the left and one to the right (such as for a [[Railway switch#Wye switch|wye switch]]), or both tracks may curve, with differing [[radius|radii]], while still in the same direction. Switches consume a relatively high proportion of a railway maintenance budget.<ref>{{Cite journal |last1=Shih |first1=Jou-Yi |last2=Weston |first2=Paul |last3=Entezami |first3=Mani |last4=Roberts |first4=Clive |date=1 June 2022 |title=Dynamic Characteristics of a Switch and Crossing on the West Coast Main Line in the UK |journal=Railway Engineering Science |volume=30 |issue=2 |pages=183–203 |doi=10.1007/s40534-021-00269-4 |s2cid=246422034 |issn=2662-4753 |doi-access=free |bibcode=2022RailE..30..183S }}</ref>