Spacing of Multiple Culverts

Spacing between multiple culverts

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)
Round Pipes
< 2.0 1.0
2.0 – 6.0 Diameter/2
> 6.0 3.0
Pipe Arches
< 3.0 1.0
3.0 – 9.0 Span/3
9.0 – 16.0 3.0
All Spans 2.0

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.


About Bernie Roseke

Bernie Roseke, P.Eng., PMP, is the president of Roseke Engineering. As a bridge engineer and project manager, he manages projects ranging from small, local bridges to multi-million dollar projects. He is also the technical brains behind ProjectEngineer, the online project management software for engineers. He is a licensed professional engineer, certified project manager, and six sigma black belt. He lives in Lethbridge, Alberta, Canada, with his wife and two kids.


  1. Bernie – I must say thank you. Your concise and very nicely organized discussion regarding culvert design is appreciated by myself, and I am sure by many others, even if they haven’t written and let you know. Thanks for taking the time.

    Best regards

    Jack Akin, MS, PE

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