(a) Upon a complaint in writing made against any common carrier, except a motor carrier holding a certificate of public service, governed by this act that any of the rates or joint rates, fares, tolls, charges, rules, regulations, classifications or schedules of such common carrier are in any respect unreasonable, unfair, unjust, unjustly discriminatory or unduly preferential, or both, or that any regulation, practice or act whatsoever affecting or relating to any service performed or to be performed by such common carrier for the public, is in any respect unreasonable, unfair, unjust, unreasonably inefficient or insufficient, unjustly discriminatory or unduly preferential, or that any service performed or to be performed by such common carrier for the public is unreasonably inadequate, inefficient, unduly insufficient or cannot be obtained, the commission may proceed, with or without notice, to make such investigation as it deems necessary.

No order changing such rates, joint rates, tolls, charges, rules, regulations and classifications, schedules, practices or acts complained of shall be made or entered by the commission without a formal public hearing in accordance with the provisions of the Kansas administrative procedure act, of which due notice shall be given by the commission to such common carrier or to such complainant or complainants, if any. Any public investigation or hearing which the commission shall have power to make or to hold may be made or held before any one or more commissioners. All investigations, hearings, decisions and orders made by a commissioner shall be deemed the investigations, hearings, decisions and orders of the commission, when approved by the commission.

(b) The commission shall have power to require common carriers, except a motor carrier holding a certificate of public service, to make such improvements and do such acts as are or may be required by law to be done by any such common carrier.