All bidders for the erection and repair of bridges and approaches thereto and for the building of culverts and improvements on roads, when the cost of such erection, repair, building, or improvement shall exceed one hundred dollars, shall be required to bid separately on each different kind and class of bridge with approaches thereto and on each culvert or improvement on roads. The lowest and best bidder on each kind or class of bridges, culverts, or improvements shall be awarded a contract for the same or all bids on the same shall be rejected. The term bridge shall be understood to include both superstructure, substructure, and approaches as herein defined. All bridges constructed entirely of wood shall be considered as constituting a single class, and each different length or style of metal or combination bridge shall constitute a separate class. The county board shall award the contract for building all the same kind and class of bridges, approaches, and culverts that may be required during the year to the lowest and best bidder on such bridges, approaches, and culverts, the object of this section being to give the county board full power to disregard blanket or collective bids. The lowest and best bidder shall enter into a bond with good and sufficient surety or furnish an irrevocable letter of credit, a certified check upon a solvent bank, or a performance bond in a guaranty company qualified to do business in Nebraska in accordance with the provisions of section 39-825.