Except as otherwise provided in Section 9-2-117, within 30 days after the final completion and, where required, acceptance of the work, as provided in Section 9-2-112, the board of local improvements shall have the cost thereof, including the cost of engineering services, certified in writing to the court in which the assessment was confirmed, together with an amount estimated by the board to be required to pay the accruing interest on bonds or vouchers issued to anticipate collection. Thereupon, if the total amount assessed for the improvement upon the public and private property exceeds the cost of the improvement, all of that excess, except the amount required to pay such interest as is provided for in this Division 2, shall be abated and the judgment reduced proportionately to the public and private property owners and shall be credited pro rata upon the respective assessments for the improvement under the direction of the court.
     In case the assessment is collectible in installments, this reduction shall be made so that all installments shall be equal in amount, except that all fractional amounts shall be added to the first installment so as to leave the remaining installments in the aggregate equal in amount and each a multiple of $100. If prior to the entry of the order abating and reducing the assessment the assessment has been certified for collection pursuant to the provisions of Section 9-2-76, and any of the installments of the assessment so certified for collection have become due and payable, the reduction and abatement above referred to shall be made pro rata upon the other installments. The intent and meaning of this is that no property owner shall be required to pay to the collector a greater amount than his proportionate share of the cost of the work and of the interest that may accrue thereon.