Modern pipeline construction includes many techniques for safely burying the pipe beneath watercourses or other obstacles with minimal environmental impact. Situations often occur, however, where bringing the pipe above-ground to cross an obstacle on a purpose-built bridge may be necessary or preferred. Such aerial crossings are often used for steep-sided deep canyons, streams with sensitive aquatic habitat, rivers with shifting or unstable beds or deep scour potential, and where sub-surface conditions are unsuitable for horizontal directional drilling.

This paper explores situations where an aerial crossing may be called for and outlines various structure types that may be used, including girder bridges, space trusses, and cable-supported bridges. Factors affecting selection of structure type are discussed, along with design criteria, pipe support methods, expansion provisions, durability, and inspection access. General construction issues are also covered, including access requirements, foundation considerations, fabrication, methods of erecting superstructures, and pipe installation.

Examples are provided of aerial crossings for gas, oil, and water pipelines that have been constructed in the past several decades, as well as crossings now under construction or being designed.

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