Whenever the council of any city having a population of more than 100,000 seeks to acquire land for projecting roads, streets and avenues or for extending any of its existing roads, streets and avenues of uniform width into the territory adjacent to such city, it may acquire the necessary lands as permitted by § 15.2-1800; however, no such land shall be acquired except within five miles from the corporate limits, and the proposed location of any such projected or extended roads, streets and avenues shall be approved by the board of supervisors of the county in which such road, street or avenue is located.