Horseshoe Curve was the Pennsylvania Railroad's solution to the problem of how to cross the Allegheny Mountains. Designed by John Edgar Thompson and Herman Haupt, this feat of engineering became operational on February 15, 1854. Since then, it has served continually as Pennsylvania's main line to the west. It was widened from one track to four between 1898 and 1900, but one track was removed in 1981, and there have been three ever since. More than 50 trains a day use the Curve, including Amtrak's Pennsylvanian.