(1)    Department of transportation to cooperate with federal agencies. The legislature of the state of Wisconsin hereby declares that the intent of this section is to assent to acts of the United States Congress heretofore and hereafter enacted, authorizing development of the national system of interstate highways located wholly or partly within the state of Wisconsin to the full extent that it is necessary or desirable to secure any benefits under such acts and to authorize the appropriate state boards, commissions, departments, and the governing bodies of counties, cities, towns and villages, and especially the department of transportation, to cooperate in the planning, development and construction of the national system of interstate highways that may be proposed for development in Wisconsin, with any agency or department of the government of the United States in which is vested the necessary authority to construct or otherwise develop or aid in the development of such system. Whenever authority shall exist for the planning and development of a national system of interstate highways of which any portion shall be located in this state, it shall be the duty of the department of transportation to make such investigations and studies in cooperation with the appropriate federal agency, and such state boards, commissions, departments and municipalities as shall have interest in such system development, to the extent that shall be desirable and necessary to provide that the state shall secure all advantages that may accrue through such interstate system development and that the interest of municipalities along such system shall be conserved.

   (2)   Routes of interstate system, state trunk highways. Upon finding by the department that the development of any proposed highway as a route of the national system of interstate highways, hereinafter designated the interstate system or interstate highways, or any portion thereof, including the laying out, construction, maintenance and operation of any part thereof as a freeway or expressway, is in the promotion of the public and social welfare of the state and for the benefit of public travel, the department is empowered and it shall have full authority to lay out, construct, operate and maintain such highway as a part of the state trunk highway system. Except as otherwise provided by this section, all provisions of law relative to the acquisition of land for highway purposes and for surveys, plans, establishing, laying out, widening, enlarging, extending, constructing, reconstructing, improving, maintaining and financing of other state trunk highways shall apply to the interstate highways undertaken in this state.

   (3)   Changes in existing highways and utilities. It is recognized that in the construction of interstate highways in this state to modern standard and design, mutually agreed upon by the department and the federal agency, to promote the public and social welfare, and benefit public travel of the state, and meet the needs of national defense, it will become necessary for the department to make or cause to be made changes in the location, lines and grades of existing public highways, railroads and public utility transmission lines and facilities.

   (4)   Laying new highways for interstate system. Upon finding and determination by the department that it is not in the public interest and that it is impractical to establish the route of the interstate system on or along an existing state trunk highway, the department is authorized and empowered to lay out and establish a new and additional state trunk highway for the interstate highway. As an interstate highway may be established, laid out and constructed on a new location as an expressway or freeway which is not on and along an existing public highway, no right of access to the highway shall accrue to or vest in any abutting property owner. As an interstate highway may be established, laid out and constructed as an expressway or freeway on and along an existing public highway, reasonable provision for public highway traffic service or access to abutting property shall be provided by means of frontage roads as a part of the interstate highway development, or the right of access to or crossing of the public highway shall be acquired on behalf of the state as a part of the interstate highway improvement project. The occupation or use of any part of an existing public highway is authorized for the construction of the interstate system. The action of the department relative to establishment, layout, location or relocation of any part of the interstate system shall be conclusive.

   (5)   Construction of grade separations at intersections. In the furtherance of the public interest and general welfare of the state and the traveling public in the development of the interstate system, the department is authorized and empowered to construct grade separations at intersections of any interstate highway with other public highways and railroads and to change and adjust the lines of public highways and if necessary combine or relocate the same to adjust traffic service to grade separation structures. The entire cost of grade separations and relocations and alterations of local roads as so determined by the department shall be a part of the construction of and financed as a part of the cost of the interstate highway. The department may by agreement with a county or municipality or by order summarily vacate or relocate any town, county, city or village highway as part of the construction of an interstate highway but shall pay any damage legally payable under existing law to any property owner directly injured by the vacation or relocation of such street or highway. The department is empowered to enter into agreement with the unit of government having jurisdiction over the local highway relocated or altered as a part of the interstate highway improvement with respect to maintenance thereof, and in the absence of mutual agreement to the contrary, such relocated or altered highway shall be maintained by the unit of government having jurisdiction thereof before it was so relocated or altered, except any parts thereof which the department determines to be useful in the operation of or for access to the interstate highway, which parts shall be maintained by the state, subject to s. 84.07 (1r), as a part of the interstate highway. The action by the department relative to vacation and relocation or combining a public highway under jurisdiction of any county, town, city or village shall be conclusive.

   (6)   Power to relocate and close highways.

      (b)    No highway of any kind shall be opened into or connected with the interstate highway by a municipality unless the department approves the same and fixes the terms and conditions on which such connection shall be made. The department may give or withhold its approval or fix such terms and conditions as it deems will best serve the public interest.

   (7)   Powers granted liberally construed. All powers granted in this section shall be liberally construed in favor of the state in the furtherance of the expeditious and orderly construction of any interstate highway project.

   (8)   Establishing freeway status. After adoption of an order by the department laying out and establishing any portion of the interstate system as an expressway or freeway, the highway described in the order shall have the status of a freeway or expressway for all purposes of this section. Such order shall not affect private property rights of access to preexisting public highways, and any property rights taken shall be acquired in the manner provided by law. No previously existing public highway shall be converted into a freeway or expressway without acquiring by donation, purchase, or condemnation the right of access thereto of the owners of abutting lands.