Switch Layout, Railroad

a device forming part of the track superstructure and serving to transfer rolling stock from one track to another. Distinctions are made between split switches, used where there is a main track and a single diverging track; equilateral switches, installed on tracks in yards employing gravity classification, where a main track bifurcates into two tracks diverging at equal angles; and the switches used in diamond crossings, which replace two single switches and allow movement in four directions.

Switches are installed in the track on special switching ties. Aside from the switch proper, which comprises two wing rails and two tongues, which engage the wheels of the rolling stock, the switch layout includes the frog and guardrails. The switches proper are connected with the main tracks by switch tracks that are classified into two types: (1) connecting track—for two adjacent tracks, and (2) ladder track—for several parallel tracks.

An important marking on the switch layout is the number appearing on the frog, which is equal to the tangent of the angle formed between the main track and the diverging track. In the USSR, frogs with markings 1/9 and 1/11 are used in stations and on track segments where trains travel at normal speeds. Frogs with markings 1/18 and 1/22 are used in high-speed segments, and those with a marking of 1/6 are used in yards employing gravity classification. The switching that is usually done electrically on a remote-control basis is one aspect of centralized traffic control. On segments with a low volume of traffic, as a rule, switching is done manually, with signals indicating the position of the switch.