yes. that option they considered but compared to TBM, Tondiarpet doesnt have much connectivity from remaining south or west so it may not be good option to have north trains there. if Tondiarpet developed RF Pandiyan cholan nellai silambu can be extended there. I dono what SR things. but rather than second ONT of TEN or SCT or MDU from TBM i feel long weeklies can start from tambaram. that makes MS free for these ONTs.