Spacing of multiple metals culverts is specified by the AASHTO LRFD Bridge Design Specifications, Section 12, “Buried Structures,” like this:
|Type of Structure||Minimum Distance Between Pipes (ft)|
|2.0 – 6.0||Diameter/2|
|3.0 – 9.0||Span/3|
|9.0 – 16.0||3.0|
The Canadian Highway Bridge Design Code, Section 12, “Buried Structures,” specifies minimum spacing of multiple culverts like this:
7.5.6 Minimum clear spacing between conduits
For multi-conduit structures, including soil-metal structures with shallow corrugations, the minimum clear spacing between adjacent conduits shall be not less than 1000 mm or one-tenth of the largest span; this requirement may be waived for concrete boxes with cement grout between the boxes. For multi-conduit soil-metal structures with deep corrugations, the minimum clear spacing between adjacent conduits shall be 1000 mm; if CLSM is used between the conduits, the minimum clear spacing may be reduced to 800 mm if the CLSM is poured to a height where its width is at least 800 mm.