Whenever the commission, after a hearing had upon its own motion or upon complaint, shall find that the rates, fares or charges in force over two (2) or more common carriers, between any two (2) points in this state, are unjust, unreasonable or excessive, or that no satisfactory through route or joint rate, fare or charge exists between such points, and that the public convenience and necessity demand the establishment of a through route and joint rate, fare or charge between such points, the commission may order such common carriers to establish such through route and may establish and fix a joint rate, fare or charge which will be fair, just and reasonable and sufficient to be followed, charged, enforced, demanded and collected in the future and the terms and conditions under which such through route shall be operated. In case the common carriers do not agree upon the division between them of the joint rates, fares or charges established by the commission over such through routes, the commission shall, after hearing, by supplemental order, establish such division. The commission shall have the power to establish and fix through routes and joint rates, fares or charges over stage or auto lines and to fix the division of such joint rates, fares or charges.