Horseshoe Curve (Pennsylvania)

Horseshoe Curve is a three-track railroad curve on the Norfolk Southern Railway's Pittsburgh Line in Blair County, Pennsylvania. The curve itself is about 2,375-foot (724 m) long and 1,300 feet (400 m) in diameter; it was completed in 1854 by the Pennsylvania Railroad as a way to lessen the grade to the summit of the Allegheny Mountains. It eventually replaced the time-consuming Allegheny Portage Railroad, the only other route across the mountains for large vehicles.

• http://en.wikipedia.org/wiki/Horseshoe Curve (Pennsylvania)