Culverts consisting of more than one box are useful in wide channels where the constriction or concentration of flow must be kept to a minimum. Alternatively, low roadway embankments offering limited cover may require a series of small openings. In addition, the situation may require separating the boxes to maintain flood flow distribution. As a general recommendation, where a culvert consists of more than one barrel, shapes of uniform geometry and roughness characteristics should be used to maintain uniform flow distribution. Locations where debris flow may obstruct the culvert entrance may be better served with a clear span bridge.

Certain situations warrant placing boxes at various elevations. Placing one box at the natural stream flowline and placing additional boxes slightly higher is good practice for the following reasons: