Eastbound Pennsylvanian on Horseshoe Curve, 2016. — Amtrak: History of America's Railroad

Horseshoe Curve - An Appreciation

Sand Patch Grade - Wikipedia

Pennsylvanian stopped at Harrisburg, 2016. — Amtrak: History of America's Railroad

Pennsylvania Railfanning, August 1994: Horseshoe Curve Pusher Start, Part 1

World Famous Horseshoe Curve

Early Amtrak trains in color

Destination Pennsylvania: A trip to the World Famous Horseshoe Curve

On Board the Pennsylvanian — Amtrak: History of America's Railroad

Bennett Levin Pennsy E units

History Blog

21 Horseshoe Curve Pennsylvania Stock Photos, High-Res Pictures, and Images - Getty Images

Keystone Corridor - Wikiwand

Pittsburgh Line Adventures 2001-2015 - Empire Of Rails - Road Trips

Photography, by Nicholas Sharrett