(a) Upon complaint in writing of any person, firm or corporation or association, or of any mercantile, agricultural or manufacturing society, or of any body politic or municipal organization, that any of the rates, fares, charges or classifications, or any joint rate or rates are in any respect unreasonable or unjustly discriminatory, or that any regulation or practice whatsoever affecting the transportation of persons or property or any service in connection therewith, is in any respect unreasonable or unjustly discriminatory, or that any service is inadequate, the commission shall notify the common carrier complained of that complaint has been made and shall furnish a copy of the said complaint with said notice, and 20 days after such notice has been given the commission may proceed to investigate the same as hereinafter provided. Before proceeding to make the investigation, the commission shall give the said common carrier and the complainants at least 10 days’ notice of the time and place when and where such matters will be considered and determined, and said parties shall be entitled to be heard and shall have process to enforce the attendance of witnesses. Such hearings may be continued from time to time in the discretion of the commission. If, upon such investigation, the rate or rates, joint rate or rates, fares, charges or classifications, regulation, practice or service complained of shall be found to be unreasonable, inadequate or unjustly discriminatory, the commission shall have power to and it shall determine and by order fix and order substituted therefor, such rate or rates, joint rate or rates, fares and charges, as is or are just and reasonable, and which shall be the maximum to be charged in the future, and such classifications, regulation, practice or service as is or are just, reasonable and adequate, and which shall be imposed and followed or service rendered in future in lieu of that found to be unreasonable, inadequate or unjustly discriminatory, and in either case the commission shall make an order that the common carrier cease and desist from such violation, and shall conform to the regulation and practice so prescribed, and it shall cause a certified copy of each such order to be delivered to an officer or station agent of the common carrier affected thereby, which order shall, of its own force, take effect and become operative 20 days after the service thereof. All common carriers to which the order applies shall, on or before the date when such order becomes effective, make such changes in schedules on file as shall be necessary to make the same conform to such order, and no change shall within 2 years thereafter be made by any such common carrier in any such rates, fares or charges, or in any such joint rate or rates, without the approval of the commission. Certified copies of all other orders of the commission shall be delivered to the common carriers thereby affected in like manner, and the same shall take effect within such times thereafter as the commission shall prescribe;

  (b) The commission may, when the complaint is made of more than 1 rate or charge, order separate hearings thereon, and may consider and determine the several matters complained of separately and at such times as it may prescribe. No complaint shall of necessity at any time be dismissed because of the absence of direct damage to the complainant;

  (c) Whenever the commission shall believe that any rate or rates or charge or charges may be unreasonable or unjustly discriminatory, or that any service is inadequate, and that any investigation relating thereto should be made, it may, upon its own motion, investigate the same. Before making such investigation, it shall present to the common carrier a statement in writing, setting forth the rate or charge to be investigated. Thereafter, on 10 days’ notice to the common carrier of the time and place of such investigation, the commission may proceed to investigate such rate or charge in the same manner and make like orders in respect thereto as if such investigation had been made upon complaint;

  (d) This section shall be construed to permit any common carrier to make complaint of like effect as though made by any person, firm, corporation or association, mercantile, agricultural or manufacturing society, body politic or municipal organization;

  (e) The commission may, after hearing on a complaint, establish through routes and joint rates as the maximum to be charged and the terms and conditions under which such through routes shall be operated when the common carriers complained of have refused or neglected to voluntarily establish such through routes and joint rates: Provided, No reasonably satisfactory through route and joint rate exist. Whenever the common carrier or common carriers, in obedience to an order of the commission or otherwise, in respect to joint rates, fares or charges, shall fail to agree among themselves upon the apportionment or division thereof, the commission may after hearing make a supplemental order prescribing the just and reasonable proportion of such joint rate, fare or charge to be received by each common carrier party thereto, which order shall take effect as part of the original order.