Yes you are right, for PDKT road is fine and KKDI also, from TJ or TPJ, depending on the availability of trains. As of now, four laning has been going on @ full pace after PDKT in the Chettinad area. This area has always been the spot of bother as it has been stretching the travel time by that extra hour. Once it gets over, even road connectivity to MAS will be great, can drastically reduce the running time (under 8 hours) and be a competitor to Boatmail (my personal preference as Sethu's timings are not that convenient.