Upon establishing an authority, the county in which the authority is located shall grant to the authority the right to use any space below the plot of ground used as a courthouse site and such portion of the surface of such plot not then used by the county for a courthouse. The city shall likewise grant to the authority the right to use the space below the surface of the streets abutting on such courthouse site including the street intersections connecting such streets. The governing bodies of the county and city shall have the authority to execute the required grants without a vote of the electorate or any authorization other than that contained in the Parking Authority Law. All such grants shall be for a period of fifty years. The authority may also acquire by lease, purchase, gift, grant, or any lawful manner, such adjoining privately owned property as may be necessary or convenient for the exercise of its powers for the construction of entrances to or exits from its facilities.