This document provides an accepted terminology for switch and crossing work. With the assistance of diagrams, the various components are given definitions, and these specific names are regarded as obligatory. The definitions cover the constituent parts and design geometry of switch and crossing work. Additional terminology of a more specific nature will be defined in the relevant part of the series. The present definitions set out the terms most generally used for the geometrical form and the construction of switches and crossings, omitting those of too special a nature.