Culvert

A culvert is a drain or pipe that allows water to flow under a road, railroad, trail, or similar obstruction. Culverts differ from bridges mainly in size and construction. Culverts are generally smaller than bridges, ranging from 0.3-metre (1 ft) pipes to larger reinforced concrete structures. Culverts are typically surrounded by soil.

For legal purposes, US structures with total spans under 20 feet (6.1 m) are considered culverts, and longer structures are bridges. When boxes or pipes are placed side-by-side to create a width of greater than twenty feet, the culvert is defined as a bridge in the United States. This is a requirement of the federal bridge inspection standards and ensures that the culvert is inspected on a regular basis.