The state highway commissioner, subject to the approval of the advisory board of the state highway commissioner and state administrative board is hereby authorized to change, alter or abandon the location of any portion of any trunk line highway now established or which may hereafter be established by legislative authority whenever such change, alteration or abandonment will, in their opinion, best serve the public interest and will not increase the trunk line mileage: Provided, That the state administrative board shall, before approving the abandonment of any portion of a state trunk line highway, hear the objection of any county road commissioners or the governing body of any township, city or village to whose jurisdiction such portion of state trunk line highway would return if abandoned and such county road commission or the governing body of any township, city or village shall be given 30 days’ notice by the secretary of the state administrative board of such hearing of abandonment. Any mileage saved by such change, alteration or abandonment of location may be used in the establishment of new trunk lines on routes to be determined by the state highway commissioner, subject to the approval of the advisory board of the state highway commissioner and state administrative board.