This news was revealed by Mr. Murli in blog /blog/post/71140
Following is the gist of the framework of the new 5 digit numbering system which was implemented in all PRS systems by Dec 20, 2010
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This will be the digit allocation
0...
more... - For Specials and limited edition trains.
1 - For all Mail/Express including Duronto, Rajdhani, Shatabdhi, JS, SK, Jan sadharan, GR, SF trains, the digit 1 will be prefixed with the existing 4 digit train numbers
2 - Whenever digit 1 is exhausted (as mentioned above), digit 2 will be used
3 - Suburban trains for Kolkata
30XXX - 37XXX (Eastern Railway)
38XXX - 39XXX (South Eastern Railway)
4 - Suburban trains for Chennai, Delhi and Secunderabad
Chennai Suburban 40XXX - 44XXX
Delhi Suburban 45XXX - 46XXX
Secunderabad Suburban - 47XXX
Reserved 48XXX - 49XXX
5 - For all passenger trains with conventional coaches
6 - For all passenger trains with MEMU
7 - For all passenger trains with DEMU/Rail car
For trains starting with 5, 6 and 7, the second digit determines the zone and third digit determines the division and last 2 digit is for trains
8 - Reserved
9 - Suburban trains for Mumbai
90XXX - 94XXX - Western Railway
95XXX - 99XXX - Central Railway