Tamilnadu has a very well planned network of railways, with two Main lines and regular connections and crossovers between the two lines. In terms of providing good coverage, this is far, far better than AP or KA where the routes are fragmented. Almost all major places in TN are connected to each other with more or less the shortest route possible, unlike AP and KA where quite a few regions are connected by round-about routes only and practically every major terminus in the state has a train to Madras Egmore or Central.
What TN needs to do is utilize the cross lines ( VM-KPD, SA-Cuddalore, SA-Dindigul) and the branch lines in the Delta regions more. Acouple of...
more... new lines, like Hosur-Krishnagiri-JTJ and JTJ-Tiruvannamali can be of some use, but to be honest, TN has enough routes to provide a very, very good coverage. The existing routes just need to be utilized more.