The Department of Highways¹ and municipalities may enter into agreements with the board, or Federal agencies with the approval of the board, to relocate roads, streets, bridges, and viaducts necessitated by the construction of any State or Federal flood control works and improvements; and may agree therein to construct new roads, streets, bridges, and viaducts, and pay the cost of the same, or any part thereof, from the Motor License Fund or municipal moneys without any charge or only part of the cost charged against the moneys in the General Fund Appropriations for Flood Control Projects. The board may consent in any such agreement to pay the whole or any part of the cost of constructing such relocated roads, streets, bridges, and viaducts from the moneys in the General Appropriations for Flood Control Projects. Such relocated roads, streets, bridges, and viaducts may be constructed by the Department of Highways or by contract let by said department, or the municipality or by the board or by a Federal agency as may be agreed upon. Relocation of State highways shall be made by plans properly approved as is required by law for the relocation of State highway routes, and may be made without regard to terminal or intermediate points mentioned in the law establishing such routes. The portions of State highway routes supplied by such relocations may be abandoned by the Secretary of Highways² in the manner provided by law, whereupon said abandoned portions of State highway routes shall revert to the authorities responsible for the maintenance of the public road or highway prior to its having been established as a State highway. Where any State highway route, or part thereof, shall become inundated by the waters of any flood control reservoir, or shall become unnecessary for public use and travel, or burdensome or dangerous due to the construction of any flood control reservoir, the Secretary of Highways, with the approval of the Governor, may abandon as a State highway such State highway route, or part thereof. The Secretary of Highways may also at any time, by and with the consent of the local authorities, by written order declare the portion or portions of road or roads so abandoned to be vacated and closed to public use and travel and no longer a public road, without limitation because of the length of the road to be vacated.