(a) General rule.--The commission may, in any proceeding involving the rates of a public utility, except a proceeding involving a general rate increase, brought either upon its own motion or upon complaint, after reasonable notice and hearing, if it be of opinion that the public interest so requires, immediately fix, determine, and prescribe temporary rates to be charged by such public utility, pending the final determination of such rate proceeding. Such temporary rates, so fixed, determined, and prescribed, shall be sufficient to provide a return of not less than 5% upon the original cost, less accrued depreciation, of the physical property, when first devoted to public use, of such public utility, used and useful in the public service, and if the duly verified reports of such public utility to the commission do not show such original cost, less accrued depreciation, of such property, the commission may estimate such cost less depreciation and fix, determine, and prescribe rates as hereinbefore provided.

(b) Exception where records unavailable.--If any public utility does not have continuing property records, kept in the manner prescribed by the commission under the provisions of section 1702 (relating to continuing property records), then the commission, after reasonable notice and hearing, may establish temporary rates which shall be sufficient to provide a return of not less than an amount equal to the operating income for such prior calendar, fiscal or other year as the commission may deem proper, to be determined on the basis of data appearing in the annual report of such public utility to the commission for such prior year as the commission may deem proper, plus or minus such return as the commission may prescribe from time to time upon such net changes of the physical property as are reported to and approved for rate-making purposes by the commission. In determining the net changes of the physical property, the commission may, in its discretion, deduct from gross additions to such physical property the amount charged to operating expenses for depreciation or, in lieu thereof, it may determine such net changes by deducting retirements from the gross additions. The commission, in determining the basis for temporary rates, may make such adjustments in the annual report data as may, in the judgment of the commission, be necessary and proper.

(c) Periodicity of rates.--The commission may fix, determine, and prescribe temporary rates every month, or at any other interval, if it be of opinion that the public interest so requires, and the existence of proceedings begun for the purpose of establishing final rates shall not prevent the commission from changing every month, or at any other interval, such temporary rates as it has previously fixed, determined, and prescribed.

(d) Excessive rates.--Whenever the commission, upon examination of any annual or other report, or of any papers, records, books, or documents, or of the property of any public utility, shall be of opinion that any rates of such public utility are producing a return in excess of a fair return upon the fair value of the property of such public utility, used and useful in its public service, the commission may, by order, prescribe for a trial period of at least six months, which trial period may be extended for one additional period of six months, such temporary rates to be observed by such public utility as, in the opinion of the commission, will produce a fair return upon such fair value, and the rates so prescribed shall become effective upon the date specified in the order of the commission. Such rates, so prescribed, shall become permanent at the end of such trial period, or extension thereof, unless at any time during such trial period, or extension thereof, the public utility involved shall complain to the commission that the rates so prescribed are unjust or unreasonable. Upon such complaint, the commission, after hearing, shall determine the issues involved, and pending final determination the rates so prescribed shall remain in effect.

(e) Effect and adjustment of rates.--Temporary rates so fixed, determined, and prescribed under this section shall be effective until the final determination of the rate proceeding, unless terminated sooner by the commission. In every proceeding in which temporary rates are fixed, determined, and prescribed under this section, the commission shall consider the effect of such rates in fixing, determining, and prescribing rates to be thereafter demanded or received by such public utility on final determination of the rate proceeding.

Cross References. Section 1310 is referred to in sections 1308, 1309 of this title.