Iowa Code 309.36 – Nature of survey

Bridge: includes any structure including supports, erected over a depression or an obstruction, such as water, a highway, or railway. See Iowa Code 309.1
Culvert: includes any structure not classified as a bridge which provides an opening under any roadway, except that this term does not include tile crossing the road, or intakes thereto, where the tile are a part of a tile line or system designed to aid subsurface drainage. See Iowa Code 309.1
road: include public bridges, and may be held equivalent to the words "county way" "county road" "common road" and "state road". See Iowa Code 4.1

The engineer’s survey shall be on the basis of the permanent improvement of said roads, as to bridge, culvert, tile, and road work.