Nomenclature
Trains are sorted into various categories that dictate the number of stops along their route, the priority they enjoy on the network, and the fare structure. Each express train is identified by a five-digit number, the first digit as 1 and 2 for long-distance Express trains. If the first digit is 0, then the train is a Special. The first digit as 5 denotes a passenger train. The second digit indicates the zone that operates the train, the third the division within the zone that controls the train and is responsible for its regular maintenance and cleanliness, and the last two digits are the train's serial number. The system was changed from four digits from 20 December 2010, in order to accommodate an increasing number of trains.
For super-fast trains, the second digit is always 2 (the first remains 1 or 2), the third digit is the zone, the fourth is the division and only the last digit is the serial number within the division. Trains travelling in opposite directions along the same route are usually labelled with consecutive numbers. However, there is considerable variation in train numbers and some zones, such as Central Railway, has a less systematic method for numbering trains. Most express trains also have a unique name that is usually exotic and taken from landmarks, famous people, rivers and so on.
Read more about this topic: Rail Transport In India