(a) When two (2) or more cities and counties shall adopt joint planning cooperation by ordinance, resolution, rule, or order, there shall be established a joint planning commission for the metropolitan area or region comprising the area coterminous with the areas of planning jurisdiction of the cities or counties cooperating jointly.
(b) A joint planning agency for the metropolitan area or region may be empowered to carry into effect such provisions of state law relating to planning which are authorized for the joining cities or counties and which each may, under existing laws, separately exercise and perform.
(c) Any other public authority or agency which operates within, wholly or in part, the area covered by this joint planning cooperation may likewise join with the cooperating cities or counties in cooperative planning through resolution of its governing board or commission.