Using JOSM with Opencyclemap I find a lot of streams flowing up the mountain!!

The NH-length in Karnataka is 6434km(OSM) and 6502km (MORTH. My calculatons take care of dual-carriage parts and road parts that are shared by two NHs (no double counting). I created for each NH-road seperate relations and calculate the length with the relation analyser. If the mapping is precise, than my calculations are also precise. A little problem is that the state boundaries are not mapped excatly. And it’s not clear what to do with NHs in big cities without a ref-tag. Does Morth count these roads??

Your statewise length of the NHs is completely out of date or full of errors. See the wiki-page for exact values. http://wiki.openstreetmap.org/wiki/National_Highways_%28statewise%29