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Horseshoe Curve

Altoona, Pennsylvania
Constructed between 1847 and 1854

Claim to Fame: The Horseshoe Curve of the Pennsylvania Railroad was 549 meters across and 805 meters long with a 1.8 percent grade, which eliminated the Portage Railroad’s 10 incline planes and greatly encouraged east-west trade crossing the Allegheny Mountains. 

Horseshoe Curve 
Courtesy Flickr/Train Pix

"This day commences the running of the regular trains upon a continuous road through the tunnel of the Allegheny Mountain, thereby avoiding the dangerous inclined planes, about which many have been the complaints and interruptions. The time between Philadelphia and Pittsburg is thus reduced to fifteen hours; and with the improvement a reduction in the fare has taken place."

Democratic Union, Harrisburg, February 15, 1854 

One of the earliest and most impressive of America's great railroad engineering feats, the Horseshoe Curve was built as a means of overcoming a straight-line grade over the geological feature known as the Allegheny Escarpment or Allegheny front, which separates the ridge-and-valley section of Pennsylvania (on the east) from the Allegheny Front (on the west). Such a straight-line route would have made commercial railroad operations infeasible from both and economic and technical standpoint. This relatively sharp curve on the Philadelphia-Harrisburg-Pittsburgh main line of the Consolidated Rail Corporation was built entirely by manual means - picks and shovels, powder and mules and still ranks among the best train-watching spot anywhere. 

The Curve opened a through route from Philadelphia to the west, restoring to that city some of the port trade that previously had been siphoned off to Baltimore and New York. In addition to encouraging commercial trade, the Curve spurred travel and immigration. It has been a major economic gateway for commerce since it opened and still carries approximately 60 trains a day carrying tons of materials between Pittsburgh and Philadelphia.