Group 1 - The naming rules for train numbers are significant, with specific letters indicating different types of trains, such as G for high-speed trains, C for intercity trains, D for动车组 trains, Z for direct express trains, T for express trains, and K for fast trains [1] - Train number assignment is closely related to the direction of travel, with even numbers assigned to trains heading towards Beijing (upward direction) and odd numbers for those traveling away from Beijing (downward direction) [3]