Horseshoe Curve is a semi-circle shaped section of railroad tracks built by the Pennsylvania Railroad to cross the Allegheny Mountains. Completed in 1854, the Horseshoe Curve was an engineering triumph that opened up east-west travel for passenger and freight trains. It made such a significant impact on United States history that in 1966, the curve earned its status as a National Historic Landmark. It is listed on the National Register of Historic Places and it will be preserved and protected by the United States government. About 50 passenger or freight trains travel through the Horseshoe Curve each day.
The Allegheny Mountains in central Pennsylvania provided a significant barrier for commerce and travel to the west. Railroad engineers set out to connect the east coast city of Philadelphia with the city of Pittsburgh in the western half of the state of Pennsylvania. Engineers were able to safely lay railroad tracks through most of the mountainous terrain. Five miles (8 km) west of the city of Altoona, Pennsylvania, the terrain became too steep.
Railroad engineers debated on the best way to proceed to Altoona. A tunnel through the mountains would have been expensive and taken many years to construct. To build railroad tracks over the mountains would have required unsafe increases in elevation. For a train to travel safely, the elevation grade of the tracks cannot exceed 1.8 percent, or a rise of 1.8 feet (0.55 meters) for every 100 feet (30.48 meters).
In the early 1850s, railroad engineer J. Edgar Thompson was able to design the Horseshoe Curve with an elevation grade of one foot (0.3 meters) for every 100 feet (30.48 meters). The tracks ran along the base of the mountain and then crossed a ravine before circling back in the original direction. Completed within a two-year period, a single track opened for rail traffic in 1854. As traffic increased, three new tracks were added.
Tourists and train enthusiasts soon began traveling to the site of Horseshoe Curve to view the tracks and watch the trains travel around the mountain. In 1992, the railroad, in conjunction with the National Park Service, opened a visitor’s center and a parking lot at the base of the tracks. Visitors can enjoy the scenic views of the mountains and landscape by taking a small inclined railcar up the steep hill from the parking lot to the tracks. The tracks can also be reached on foot by climbing a steep walk of 194 steps. A trackside picnic area makes the Horseshoe Curve a popular destination.