Before the whole or any part of any interstate bridge shall be closed, either pursuant to an agreement between the department and an adjoining state or otherwise, the party closing such bridge shall notify in writing the proper authorities of the department, the adjoining state, and, as may be necessary, the political or governmental subdivisions of the State of Nebraska and the adjoining state directly concerned, of the intent to close the bridge, the area of the bridge which will be closed, the date and time of such closing, the approximate amount of time such area will be closed, and the route of any detours established; Provided, that such notice shall not be required when the whole or any part of an interstate bridge is closed for emergency maintenance under the authority of section 39-8,115.