Construction of the Pennsylvania Railroad's Atglen and Susquehanna Branch along the western boundary of Manor Township began in 1903 in terrain where the Susquehanna River had carved steep cliffs and left little room for a modern two-track freight line. The project built on the earlier Columbia and Port Deposit Railroad, completed into Columbia, Pennsylvania, from the south in 1877 under Pennsylvania Railroad control, whose primarily single-track route along the river's eastern shore was often threatened by high water within Manor Township. By creating the A&S, the railroad elevated the C&PD, reduced curvature and grades, and established two separate freight roads where there had barely been room for one. From 1903 to 1906, H. S. Kerbaugh Co coordinated extensive drilling and blasting along the river, at times employing as many as 3,000 laborers who scaled unstable slopes by rope line, drilled vertical holes up to 133 feet deep and horizontal holes up to 35 feet deep, and used dynamite, blasting powder, and electric current to dislodge rock and loam and grade it to the water's edge. In July 1905 alone, a month of drilling used 225 tons of explosives to remove an estimated 240,000 cubic yards of material in a single blast. Two new rail shelves gradually emerged on the east bank of the river, visible where their spans cross the mouth of the Conestoga River on the Safe Harbor Bridge. North of Manor Township, the A&S crossed the Susquehanna on the Pennsylvania Railroad's Shocks Mill Bridge at Marietta and continued to the Enola Classification Yard west of Harrisburg, and from near Washington Boro to Atglen there were no grade crossings. By 1941, this low-grade freight route carried a daily average of 29 eastbound freights with 2,424 cars and 23 westbound freights with 2,224 cars, making the Atglen and Susquehanna Low Grade one of the largest civil engineering projects in Lancaster County.