Bridges, numbering; duties of county board; highway history, highway superintendent to keep.

For the purpose of assisting the county highway superintendent in making and keeping the bridge record, the county board shall adopt a system of numbering all county bridges, and place and keep on each bridge a plain and substantial number, and furnish to the county highway superintendent a complete inventory of all bridges so numbered. The superintendent shall keep all maps, charts, plans, and specifications of such roads and bridges so as to preserve, as nearly as possible, a complete history of the roads of the county.