The Horseshoe Curve is a three-track railroad curve on Norfolk Southern Railway's Pittsburgh Line in Blair County, Pennsylvania, United States. The curve is roughly 2,375 feet (700 m) long and 1,300 feet (400 m) in diameter. Completed in 1854 by the Pennsylvania Railroad as a way to reduce the westbound grade to the summit of the Allegheny Mountains, it replaced the time-consuming Allegheny Portage Railroad, which was the only other route across the mountains for large vehicles. The curve was later owned and used by three Pennsylvania Railroad successors: Penn Central, Conrail, and Norfolk Southern. Horseshoe Curve has long been a tourist attraction. A trackside observation park was completed in 1879. The park was renovated and a visitor center built in the early 1990s. The Railroaders Memorial Museum in Altoona manages the center, which has exhibits pertaining to the curve. The Horseshoe Curve was added to the National Register of Historic Places and designated as a National Historic Landmark in 1966. It became a National Historic Civil Engineering Landmark in 2004.
Location and design
Horseshoe Curve is 5 miles (8 km) west of Altoona, Pennsylvania, in Logan Township, Blair County. It sits at railroad milepost 242 on the Pittsburgh Line, which is the Norfolk Southern Railway Pittsburgh Division main line between Pittsburgh and Harrisburg, Pennsylvania. Horseshoe Curve bends around a dam and lake, the highest of three Altoona Water Authority reservoirs that supply water from the valley to the city. It spans two ravines formed by creeks: Kittanning Run, on the north side of the valley, and Glenwhite Run, on the south. The Blair County Veterans Memorial Highway (SR 4008) follows the valley west from Altoona and tunnels under the curve. Westbound trains climb a maximum grade of 1.85 percent for 12 miles (19 km) from Altoona to Gallitzin. Just west of the Gallitzin Tunnels, trains pass the summit of the Allegheny Mountains, then descend for 25 miles (40 km) to Johnstown on a grade of 1.1 percent or less. The overall grade of the curve was listed by the Pennsylvania Railroad as 1.45 percent; it is listed as 1.34 percent by Norfolk Southern. The curve is 2,375 feet (724 m) long and about 1,300 feet (400 m) across at its widest. For every 100 feet (30 m), the tracks at the Horseshoe Curve bend 9 degrees 15 arc minutes, with the entire curve totaling 220 degrees. The rise of a westbound train through the curve can be described in several ways. One measurement is from the point where the rails north of the curve start to bow out to a point on the line directly south, across the original Kittanning Reservoir: across this north–south distance of 1,119 feet (340 m), a train rises from 1,601 feet (490 m) above sea level to 1,660 feet (510 m). Another measurement is from the point where the rails coming west out of Altoona make their first detour north to the curve, to a point across Lake Altoona where the rails begin their one-mile straight run south before turning west to the Gallitzin Tunnels; this measurement encompasses the entire Curve structure, including both reservoirs built in its bounds to protect the curve from flooding. Across this north-south distance of 1,006 feet (310 m), a westbound train rises from 1,473 feet (450 m) to 1,706 feet (520 m). This latter rise—133 vertical feet in 1,006 linear feet—is a 13.2% grade, completely unascendable by conventional railroads, which usually stick to grades of 2.2% or less. Each track consists of 136 pounds per yard (67.5 kg/m), welded rail. Before dieselization and the introduction of dynamic braking and rail oilers, the rails along the curve were transposed—left to right and vice versa—to equalize the wear on each rail from the flanges of passing steam locomotives and rail cars, thereby extending their life.
History
Origin In 1834, the Commonwealth of Pennsylvania built the Allegheny Portage Railroad across the Allegheny Mountains to connect Philadelphia and Pittsburgh, as part of the Main Line of Public Works. The Portage Railroad was a series of canals and inclined planes and remained in use until the mid-19th century. The Pennsylvania Railroad was incorporated in 1847 to build a railroad from Harrisburg to Pittsburgh, replacing the cumbersome Portage Railroad. Using surveys completed in 1842, the state's engineers recommended an 84-mile (135 km) route west from Lewistown that followed the ridges with a maximum grade of 0.852 percent. But the Chief Engineer for the Pennsylvania Railroad, John Edgar Thomson, chose a route on lower, flatter terrain along the Juniata River and accepted a steeper grade west of Altoona. The valley west of Altoona was split into two ravines by a mountain; surveys had already found a route with an acceptable grade east from Gallitzin to the south side of the valley, and the proposed Horseshoe Curve would allow the same grade to continue to Altoona.
Construction
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