Except for railroad-highway grade separations and single lane one directional ramp bridges, and except as hereinafter provided, all bridges and culverts on any trunk highway, county state-aid highway, or municipal state-aid street hereafter established, constructed, or improved shall be at least 24 feet wide between curbs, and approaches thereto shall be at least 28 feet wide shoulder to shoulder. Nothing contained herein shall be construed to prevent the state, counties, or municipalities from performing ordinary repairs or maintenance on any such bridge or culvert less than 24 feet wide between curbs.
Upon finding it practical to do so, the commissioner may make extraordinary repairs or improvements on existing trunk highway bridges less than 24 feet wide between curbs without widening such bridges. Counties and municipalities may make extraordinary repairs or improvements on major existing bridges less than 24 feet wide between curbs, without widening such bridges, if the plans for such extraordinary repairs or improvements are first approved by the commissioner. A major bridge shall mean a bridge which, together with its approaches, is at least 75 feet in length.
Except for railroad-highway grade separations, all bridges, culverts, and approaches thereto on all other roads, except cartways, hereafter established, constructed, or improved shall be at least 20 feet wide, provided that in cases where salvaged material from a steel span bridge removed from a highway can be used in the erection of a steel span bridge on a county highway or town road, such bridge, so to be erected, may be less than 20 feet wide, but before such bridge is erected the plan shall first be approved by the commissioner.