Jackson Street Skew Arch

The Jackson Street Railroad Overpass carries CSX trains over Jackson Street in Western New York. It was originally built in 1869 and is a very rare example of a helicoidal arch. It is one of only 10 identified helicoidal arches in the United States and was the second bridge of this type in the world when it was constructed. The bridge has since been widened with concrete, although the date of the widening is unknown. It is still in use and carries thirty to forty trains per day. There is also a steel bridge adjacent to the Skew Arch which carries another rail line.

In a skew arch, the faces are not perpendicular to the abutments, which complicates the design and construction. The plan view is a parallelogram instead of a rectangle. A helicoidal arch is a type of skew arch where the masonry blocks are not parallel to the ground. The blocks are placed at an angle which makes a spiral pattern inside the arch. Calculating the geometry for this type of arch is very complicated. However, it has the benefit that all of the wedged-shaped stones that make up the arch are identical, except for the ring stones.