Horseshoe Curve

Norfolk Southern Dash-9 44CW #9135 leads a double-stack container train uphill at the famed Horseshoe Curve outside of Altoona, Pennsylvania on the Pittsburgh Line.
Carved out of the Allegheny mountains by the Pennsylvania Railroad in 1854, the curve alleviated time-consuming switch back routes used for heavy vehicles, and allowed trains to gracefully sweep thirteen hundred feet around the small valley, as they descended the 1.85% grade towards Altoona. The curve survived through the subsequent eras of Penn Central, Consolidated Rail,
and now the Norfolk Southern, being registered as a National Historic Landmark in 1966, and a National Historic Civil Engineering Landmark in 2004.