 horseshoe curve is a three-track railroad curve on the norfolk southern railway's pittsburgh line in blair county, pennsylvania. the curve itself is about  long and  in diameter; it was completed in 1854 by the pennsylvania railroad as a way to lessen the grade to the summit of the allegheny mountains. it eventually replaced the time-consuming allegheny portage railroad, the only other route across the mountains for large vehicles. the rail line has been important since its opening, and during world war ii the curve was targeted by nazi germany in 1942 as part of operation pastorius. the curve was later owned and used by pennsylvania railroad successors penn central, conrail, and norfolk southern. horseshoe curve was added to the national register of historic places and designated a national historic landmark in 1966, and became a national historic civil engineering landmark in 2004. horseshoe curve has long been a tourist attraction with a trackside observation park being completed in 1879. in the early 1990s the park was renovated and a visitor center built; the railroaders memorial museum in altoona manages the center, which has exhibits pertaining to the curve. == location and design == thumb|left|topographic map of the area around the horseshoe curve horseshoe curve is on the pittsburgh line, the norfolk southern railway pittsburgh division main line between pittsburgh and harrisburg, pennsylvania. westbound trains climb a maxim
Buildings_and_structures_in_Blair_County,_Pennsylvania Historic_Civil_Engineering_Landmarks National_Historic_Landmarks_in_Pennsylvania National_Register_of_Historic_Places_in_Pennsylvania Norfolk_Southern_Railway Pennsylvania_Railroad Rail_infrastructure_in_Pennsylvania Railway-related_listings_on_the_National_Register_of_Historic_Places Railway_lines_opened_in_1854 Transportation_in_Blair_County,_Pennsylvania Visitor_attractions_in_Blair_County,_Pennsylvania