N.D. Cent. Code § 24-08-01
If the board of county commissioners approves the construction of a bridge, the county shall proceed to advertise by publication at least once each week, for two successive weeks, in the official newspaper of the county, the plans and specifications of the proposed bridge, asking for sealed bids for the construction of the bridge to be submitted to the board of county commissioners at the next regular or special meeting of the board, at which time the board shall proceed to examine all proposals or bids. The first publication for bids must be made at least fifteen days before the meeting of the board to examine the proposals or bids. Upon the receipt of satisfactory bids, the board shall award the contract to the lowest responsible bidder, requiring the bidder to give a bond in a sum not less than the amount stipulated in the bid or contract, conditioned for the faithful compliance with the terms of the bid or contract, the bond to be approved by the board and filed in the office of the county auditor. If no satisfactory bids are received, the board may reject all bids. If all bids are rejected, the board shall readvertise for bids in accordance with this section. If the amount of the lowest responsible bid is less than fifteen thousand dollars, the board may refuse all bids received and proceed to construct the bridge under its own supervision as it deems most expedient and may enter into contracts for the labor or material to be used in the construction of the bridge.
N.D.C.C. § 24-08-01