Any 2 or more counties may by their boards of supervisors contract for the purpose of planning a system of inter-county highways, super-highways and limited access highways for such counties, and may bind themselves thereto by resolution adopted by a 2/3 vote of the board of supervisors of each county so combining, for a term of not to exceed 5 years; and when the term of any contract made hereunder shall have expired, such contract may be renewed from time to time for additional terms of not to exceed 5 years subject to the other provisions of this act.