Editing Railroad switch (section)

== Classification ==
[[File:Railroad Turnout on B&MLRR at City Point, ME.jpg|thumb|A low-speed #6 right-hand switch between a main line and a rail yard]]

The divergence and length of a switch is determined by the angle of the frog (the point in the switch where two rails cross, see below) and the angle or curvature of the switch blades. The length and placement of the other components are determined from this using established formulas and standards. This divergence is measured as the number of units of length for a single unit of separation.

In North America this is generally referred to as a switch's "number". For example, on a "number 12" switch, the rails are one unit apart at a distance of twelve units from the center of the frog.

In the United Kingdom points and crossings using chaired bullhead rail would be referred to using a letter and number combination. The letter would define the length (and hence the radius) of the switch blades and the number would define the angle of the crossing (frog). Thus an A7 turnout would be very short and likely only to be found in tight places like dockyards whereas an E12 would be found as a fairly high speed turnout on a mainline.

On the [[London, Midland and Scottish Railway]], switch curvatures were specified from A (sharpest) to F (shallowest), with the following corresponding radii:<ref>{{cite web |url=http://www.lmssociety.org.uk/assets/pdfs/permanentWay1928.pdf |title=Drawings of Standard Railway Equipment Permanent Way |date=1928 |website=The LMS Society |publisher=London Midland & Scottish Railway |access-date=6 March 2022 |pages=8–17, 55–64 }}</ref>
* B – {{convert|613|ft|m|2}} – simple [[#Crossover|crossover]] with a 1 in 8 [[#Frog (common crossing)|crossing]] angle
* C – {{convert|980|ft|m|2}} – scissors or simple crossover with a 1 in 10 crossing angle
* D – {{convert|1379|ft|m|2}} – [[Double junction|double track junction]] switch with a 1 in 12 crossing angle