Horseshoe Curve is 5 miles (8 km) west of Altoona, Pennsylvania, in Logan Township, Blair County.

[3][4] The Blair County Veterans Memorial Highway (SR 4008) follows the valley west from Altoona and tunnels under the curve.

[6] 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.

[10] Using surveys completed in 1842,[14] 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.

[15] 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.

[13] In 1879, the remaining part of the mountain inside the curve was leveled to allow the construction of a park and observation area—the first built for viewing trains.

[18] Horseshoe Curve was depicted in brochures, calendars and other promotional material; Pennsylvania Railroad stock certificates were printed with a vignette of it.

[24] The Pennsylvania pitted the scenery of Horseshoe Curve against rival New York Central Railroad's "Water Level Route" during the 1890s.

[18] A raised-relief, scale model of the curve was included as part of the Pennsylvania Railroad's exhibit at the 1893 World's Columbian Exposition in Chicago.

[25] Pennsylvania Railroad conductors were told to announce the Horseshoe Curve to daytime passengers—a tradition that continues aboard Amtrak trains.

[26] The military intelligence arm of Nazi Germany, the Abwehr, plotted to sabotage important industrial assets in the United States in a project code-named Operation Pastorius.

[27] In June 1942, four men were brought by submarine and landed on Long Island, planning to destroy such sites as the curve, Hell Gate Bridge, Alcoa aluminum factories and locks on the Ohio River.

[28] The would-be saboteurs were quickly apprehended by the Federal Bureau of Investigation after one, George John Dasch, turned himself in.

[30] During the 1954 celebration of the centennial of the opening of Horseshoe Curve, a night photo was arranged by Sylvania Electric Products using 6,000 flashbulbs and 31 miles (50 km) of wiring to illuminate the area.

[37] The K4s 1361 was removed from the curve for a restoration to working order in September 1985 and was replaced with the ex-Conrail EMD GP9 diesel-electric locomotive 7048 that was repainted into a Pennsylvania Railroad scheme.

[41] The curve remains busy as part of Norfolk Southern's Pittsburgh Line: as of 2008[update], it was passed by 51 scheduled freight trains each day, not including locals and helper engines, which can double the number.

[43][44][45] In 2012, Norfolk Southern said annual traffic passing Horseshoe Curve was 111.8 million short tons (101.4 Mt), including locomotives.