The department shall have the authority, as a last resort, to provide replacement housing when a state-aid project on the state highway system cannot proceed to actual construction because no comparable replacement sale or rental housing is available. In carrying out the relocation assistance activities, the department, with prior concurrence of the board, shall be authorized to make payments, construct or reconstruct with its own forces, cause to be constructed or reconstructed, and purchase by deed or condemnation any real property for the purposes of relocating or constructing replacement housing. The department may exchange, lease, or sell to the displaced person such replacement housing. Whenever any real property has been acquired under this Code section and thereafter the department determines that all or any part of said property or any interest therein is no longer needed for such purposes because of changed conditions, the department is authorized to dispose of such property or interest therein in accordance with subsection (b) of Code Section 32-7-4.