(1) Except as may be otherwise prescribed, a permit granted by the Regional Transport Authority of any one region shall not be valid in any other region, unless the permit has been countersigned by the Regional Transport Authority of that other region, and a permit granted in any one State shall not be valid in any other State unless countersigned by the State Transport Authority of that other State or by the Regional Transport Authority concerned: 1[ Provided that a private carrier' s permit, granted by the Regional Transport Authority of any one region with the approval of the State Transport Authority, for any area in any other region or re- gions within the same State shall be valid in that area without the countersignature of the Regional Transport Authority of the other region or of each of the other regions concerned: 2[ Provided further that where both the starting point and the terminal point of a route are situate within the same State, but part of such route lies in any other State and the length of such part does not exceed sixteen kilometres, the permit shall be valid in the other State in respect of that part of the route which is in that other State notwithstanding that such permit has not been countersigned by the State Transport Authority or the Regional Transport Authority of that other State-.] 3[ Provided also that-
(a) where a motor vehicle covered by a permit granted in one State is to be used for the purposes of defence in any other State, such vehicle shall display a certificate, in such form, and issued by such authority, as the Central Government may, by notification in the Official Gazette, specify, to the effect that the vehicle shall be used for the period specified therein exclusively for the purposes of defence; and
(b) any such permit shall be valid in that other State notwithstanding that such permit has not been countersigned by the State Transport Authority or the Regional Transport Authority of that other State.]