@Mission..suggest you take the following route.
Chennai - Vellore - Krishangiri - Dharmapuri - Thoppur - Bhavani - Perunudurai and then onto Coimbatore you would get good 4 lane roads upto Krishnagiri, and the stretch between Krishnagiri is decent even though because of work you would have diversions. Thoppur Bhavani is a very good two lane road. After Bhavani its the same NH47 which is seeing construction work so expect a lot of diversions, am not sure about post Walayar, somebody from "Naadu" can update you.
Cheers. |