Any irregular- or regular-route common carrier who or that, during any period of not less than sixty (60) consecutive days, fails or has failed to render any part of the service authorized by the common carrier’s certificate, except that for the reason that highways over which the common carrier must operate are impassable because of floods, conditions of the highways, or other reasonable causes, shall be deemed to have abandoned that part of the service authorized by the certificate; and if, after a hearing, the administrator finds that the carrier has so failed to render service in accordance with the common carrier’s certificate and not for any reason set forth in the foregoing exceptions, the common carrier’s rights thereto to the extent of the common carrier’s failure to render service shall be forfeited; and the administrator shall revoke or reissue the common carrier’s certificate subject to the resulting limitations.