What factors determine whether a direct train is available?

A direct train exists between two stations only if both stations lie on the same railway route and the train halts at both points. The railway network is divided into zones and divisions, and not all stations are connected by a single direct line. Some routes require passengers to change trains at a junction station. The availability of a direct train also depends on the category of the train superfast, express, or passenger trains and whether the railway has scheduled a halt at your specific station. Premium trains like Rajdhani and Shatabdi stop only at major stations, so they may not connect smaller towns directly.