OPERATIONS MANUAL OF NATIONAL HIGHWAYS:

ÔÇ£It shall be the responsibility of the Central Government to develop and maintain in proper repair all national highways; but the Central Government may, by notification in the Official Gazette, direct that any function in relation to the development or maintenance of any national highway shall, subject to such conditions, if any, as may be specified in the notification, also be exercisable by the Government of the State within which the national highway is situated or by any officer or authority subordinate to the Central Government or to the State Government.ÔÇØ  

Accordingly, the development and maintenance of 1238 Kms   National Highways is done by the National Highway Wing of Himachal Pradesh Public Works Department.