What do the notations such as 2-4-2 mean?
Traditionally, steam locomotives have been classified by their wheel arrangements. The system most widely used was the Whyte system. In this, the loco’s leading non-powered wheels, the (usually coupled) driving wheels, and the trailing non-powered wheels are indicated separately. Indian practice (following the UK) was to count wheels and not just the axles. Hence, ‘2-4-2’ refers to a loco with two wheels (1 axle) in the front, 4 driving (powered) wheels in the middle (2 axles) and 2 wheels (1 axle) trailing. A suffixed ‘T’ indicates a tank engine (variants include ‘ST’ for saddle tank, ‘WT’ for well tank, ‘PT’ for pannier tank, etc.). Garratts and other articulated locos are usually indicated by juxtaposing the wheel arrangements of each individual component of the compound loco: e.g., 4-8-2+2-8-4. A loco may have two or three sets of coupled powered driving axles; in which case the notation might be something like 2-8-8-2 indicating two sets of 4 driving axles each, or 2-6-6-6-2 for t
