Pigtail bridge

A spiral bridge, loop bridge, or pigtail bridge is a road bridge which loops over its own road, allowing the road to climb rapidly. This is useful in steep terrain, or where the approach road to a bridge would terminate too far from the bridge's end. The shape of the bridge forms a helix, not a spiral.

Many multi-storey car parks feature such a design as this.

In the Black Hills of South Dakota, a particular form of spiral bridge, locally called a 'pigtail bridge' was introduced in 1932 by Cecil Clyde Gideon, the self-taught superintendent of Custer State Park turned highway designer. He called them “spiral-jumpoffs”. During the planning for Iron Mountain Road, there was a need to negotiate sudden elevation drops while preserving natural features for this scenic highway; the corkscrew design allowed for a spectacular - although expensive - solution to this problem. In order to blend the bridges with their surroundings, natural materials such as local timber were used.

Most pigtail bridges were built by the Civilian Conservation Corps in the 1930s.

The Nesciobrug over the Amsterdam-Rijnkanaal in Amsterdam

Turnover bridges were a feature of some early British canals such as the Macclesfield. The boats were pulled by a horse, and in locations where the towpath crossed to the opposite bank, the spiral on one side allowed the horse to continue without detaching the tow rope. They were not universally provided as they were more expensive to build, needing to span both the canal and the towpath.

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