The numbered stations make it easier to find a particular station -- perhaps by having an index in different languages. Numbering the stations appears useful, but the two-stage code used is confusing and cluttered, as other answers have indicated.
Since all the station numbers on each line already use leading zeros, a better
solution would simply be to append the station number to the line number:
This produces a map with less complexity but the same information. All the stations on a line are still grouped together. A station numbered 318 is on line three, which is orange.
[The obvious limitation which arises when a line is extended to have more than 100 stations might be met by using letters: 398, 399, 3A0, 3A1... But even the most extensive metro system in the world (London) doesn't have lines that long.]