State Higway Mapping

How is state highway done ? What tags are used ?

See http://wiki.openstreetmap.org/wiki/India:Tags/Highway

See http://wiki.openstreetmap.org/wiki/India:Roads for progress.

One doubt on relations
http://wiki.openstreetmap.org/wiki/India:Roads/Kerala

http://www.openstreetmap.org/relation/1470508
1470508 is superset of Kerala state highways.
Can I know how many kms are tagged now ?
Is there a dynamic method ?