Crossing the Appalachian Mountains: Pennsylvania Railroad

Home » Appalachian Railroads » Pennsylvania Railroad – PRR » Crossing the Appalachian Mountains: Pennsylvania Railroad

The Iron Artery: The Pennsylvania Railroad’s Journey Over the Mountains

The completion of the Pennsylvania Railroad’s (PRR) all-rail line between Philadelphia and Pittsburgh in 1854 was a landmark achievement in American civil engineering and a pivotal moment in the nation’s industrial development. It marked a triumph of innovation and perseverance over the formidable geographic barrier of the Allegheny Mountains. Under the shrewd leadership of engineer and president John Edgar Thomson, the PRR’s continuous rail corridor supplanted the state’s slow and cumbersome hybrid canal-and-rail system. This shift dramatically expedited travel and commerce, fueling Pennsylvania’s economic rise and establishing the PRR as a model of technological and managerial excellence for the world.

The Predecessor: A Patchwork of Public Works

To truly appreciate the PRR’s achievement, one must first understand the state of transportation that preceded it. Before the PRR’s iron artery, the primary east-west link was the state-sponsored Main Line of Public Works, a complex system completed in 1834. This multi-modal corridor was a product of the canal-building era, designed to connect Philadelphia with Pittsburgh to compete with New York’s successful Erie Canal.

The Main Line was an inefficient patchwork that required travelers and cargo to undergo numerous transfers. It consisted of:

  • The Philadelphia and Columbia Railroad
  • A series of canals that followed the Susquehanna and Juniata rivers to Hollidaysburg
  • The legendary Allegheny Portage Railroad, an inclined plane railroad that hoisted canal boats over the Allegheny summit
  • Another canal system that followed the Conemaugh and Allegheny rivers to Pittsburgh

The Allegheny Portage Railroad was a technological marvel of its time, featuring ten inclined planes powered by stationary steam engines and hemp ropes to pull rail cars and boat sections up and down the mountain. It cut the travel time between Philadelphia and Pittsburgh from weeks to around four days, but its operational costs were high, and the system was vulnerable to winter freezes and frequent accidents. The cumbersome transfers at every junction made the journey agonizing for passengers and inefficient for freight.

John Edgar Thomson’s Visionary Route and the Rivers’ Role

Recognizing the limitations of the Main Line, the Pennsylvania Railroad Company was chartered in 1846 with a clear mandate: build an all-rail line to rival the state’s costly public works. Under the guidance of its first chief engineer, John Edgar Thomson, the PRR embarked on a mission to lay a permanent, reliable, and efficient rail line.

Thomson’s engineering philosophy centered on minimizing steep grades by following the natural topography of river valleys. The 400-mile main line was designed to take advantage of these natural features, following the Juniata River west from Harrisburg toward the mountains. The vast majority of the route, over 350 miles, was constructed along these relatively level valleys.

This strategic use of geography meant that while the PRR’s all-rail line avoided the use of rivers for transport (unlike the canals), it cleverly used the corridors carved by the rivers to its advantage. Rivers served as natural, ready-made pathways that dramatically eased the construction process and kept grades low.

The route itself can be roughly segmented to illustrate this balance of river-following and mountain-climbing:

  • Philadelphia to Harrisburg (approx. 105 miles): This section traverses relatively gentle terrain, running near or across the Schuylkill and Susquehanna rivers.
  • Harrisburg to Altoona (approx. 130 miles): This significant portion constitutes a majority of the total route’s length. The line follows the west bank of the Susquehanna River briefly before turning westward and hugging the winding Juniata River and its branch, the Little Juniata River, through the foothills of the Appalachians.
  • Altoona to Johnstown (approx. 37 miles): This is the heart of the mountain crossing, where the most challenging grades occur. The climb up the eastern slope to the summit at Gallitzin is approximately 12 miles long, rising at a continuous grade of around 1.8 to 1.85%. West of the summit, the line descends for about 25 miles to Johnstown, largely following the Little Conemaugh and Conemaugh rivers.
  • Johnstown to Pittsburgh (approx. 80 miles): From Johnstown, the route again follows the relatively level valleys of the Conemaugh and Allegheny rivers across the Allegheny Plateau and into Pittsburgh.

In total, while the crossing of the mountain at the summit was an intense, focused engineering challenge, the vast majority of the track mileage was laid along the practical, natural pathways of the state’s river systems.

Conquering the Summit: Horseshoe Curve and Gallitzin Tunnels

The primary challenge remained the steep Allegheny Ridge between Altoona and Johnstown. To surmount this formidable obstacle, Thomson and his engineers devised two brilliant and enduring solutions:

  • The Horseshoe Curve: Completed in 1854, the Horseshoe Curve was a revolutionary engineering feat that allowed trains to conquer the mountain’s eastern face with a gentle, manageable grade. Instead of a direct and impossibly steep ascent, Thomson designed a sweeping, 220-degree arc in the valley of Burgoon Run, allowing trains to gain elevation gradually. The construction was a Herculean effort, primarily undertaken by Irish immigrant laborers using picks, shovels, and mules to carve the tracks into the mountainside. The curve’s manageable grade of 1.85% eliminated the need for the treacherous and slow inclined planes of the Portage Railroad.
  • The Gallitzin Tunnels: At the crest of the Alleghenies, just west of the Horseshoe Curve, the PRR bored a series of tunnels to complete its passage through the mountain. The first, originally called the “Summit” and later renamed the Allegheny Tunnel, was completed in 1854. This and subsequent tunnels (a second in 1855 and a third in 1904) were carved through solid rock by tireless laborers. By passing through the mountain’s peak, the tunnels eliminated the final, arduous climb and descent of the previous system.

The Legacy of a Railroad Empire

The completion of the PRR’s main line on February 15, 1854, marked the end of the Main Line of Public Works’ dominance. In 1857, the PRR cemented its supremacy by purchasing the state’s entire public works system, cannibalizing and abandoning most of the canals and the old portage railroad. Travel time between Philadelphia and Pittsburgh was slashed to a mere 15 hours, and the line became a year-round, reliable artery for a growing nation.

The PRR’s mountain-crossing legacy extends far beyond its engineering marvels. The Horseshoe Curve became a national symbol of American ambition and ingenuity, famously featured in promotional materials and as a tourist destination. John Edgar Thomson’s strategic vision and methodical management style enabled the PRR to become the largest corporation in the world, pioneering modern corporate organizational structures. The line he forged, with its seamless integration of river valleys, innovative curves, and tunnels, remains an essential part of the U.S. rail network today, operated by Norfolk Southern and Amtrak. The Pennsylvania Railroad’s crossing of the Allegheny Mountains stands as a towering testament to human will and the power of iron to connect a continent.

For More Information – Sources and Resources

The following are excellent resources for those of you wanting to explore and learn more about the history and operation of the Appalachian Railroads. These sources of information also serve as reference and historical materials for Appalachian-Railroads.org. Much of the collective railroad history data points on this website are verified across multiple sources.

Contact Us

Would enjoy hearing from you if you have questions, suggestions, edits, or content that you are willing to share. Don’t hesitate to reach out if you have similar interests in the railroads or model railroading.

Go back

Your message has been sent

3Cs Websites

Appalachian-Railroads.org | Clinchfield.org | Southern-Railroads.org