In the case of roads, the minimum width between shoulders shall be fourteen feet with eight feet of surfacing, and in the case of bridges, which includes all decked structures, the minimum standard shall be for H-10 loading in accordance with the standards of the state department of transportation. When the standards have been prepared by the county road engineer, they shall be submitted to the county legislative authority for approval, and when approved shall be used for all road and bridge construction and improvement in the county.