The Atglen and Susquehanna Branch was built by the Pennsylvania Railroad between 1902 and 1906. The branch was built to relieve congestion on the Philadelphia to Harrisburg Main Line and the railroad's Columbia & Port Deposit line. It was designed for freight service, and minimizing the grade profile was of high importance, since freight service on the main line was hampered by relatively steep grade profiles. Thus the branch was often known simply as the "Low Grade." During construction of the A&S Branch, the existing C&PD stone bridge at the Conestoga Riverwashed out. Rather than rebuild, the C&PD bridge was combined with the A&S bridge to form a unique two-line, two-level steel viaduct known as the Safe Harbor Trestle. This bridge at the Conestoga carried the C&PD line over the river, while the A&S ran parallel and approximately above. Construction was completed and the line opened for traffic by July 1906. When combined with the railroad's Trenton Cutoff and Philadelphia & Thorndale Branch, the new line permitted the PRR to operate a low-grade bypass between Morrisville, Pennsylvania and Harrisburg. This allowed freight trains to avoid the congestion of the eastern seaboard and the steep grades of the Main Line. The line flourished with freight traffic until the decline of northeast railroads and overall reduction in traffic made the line redundant. The line survived PRR's short-lived successor Penn Central until the era of Conrail. Conrail downgraded the line, first removing the overhead catenary, then by rerouting traffic over the former Reading Company's line from Harrisburg to northern New Jersey. The last trainon the line ran in 1988. Conrail petitioned the Interstate Commerce Commission to abandon the line in 1989 and track was removed around 1990. Although trackage was dismantled prior to the 1999 breakup of Conrail by the Norfolk Southern Railway and CSX Transportation, the right-of-way had been retained due to disputes over the historical nature of the line's bridges, and passed to NS. A group called Friends of the Atglen-Susquehanna Trail had prepared to establish the line as a rail trail, but this plan was opposed by local township residents and ultimately failed. NS eventually sold the line to the seven townships through which it passes in July 2008. NS received $1 from each of the townships, although it also supplied the townships with a total of $1.4 million for bridge removal or repair. Amtrak, which received ownership of PRR's electric traction system, continues to operate the two 138 kV transmission lines that run along the A&S right-of-way. The transmission lines, utilizing the distinctive PRR catenary poles, were replaced with typical utility-style monopoles in 2012.
Modern day
After abandonment, the right-of-way was under heavy brush. The loose track ballast remained, although the ties were removed, and the surface was rough. The Pennsylvania Railroad catenary supports remained, operated by Amtrak under easement, to supply electricity from Safe Harbor Dam to the Parkesburg traction substation. They are the only remaining structure supporting railroad operations. The original transmission lines were replaced by Amtrak in 2011. See Amtrak's 25 Hz traction power system#Conestoga to Atglen transmission line. Since the right-of-way was transferred to the respective townships, about of the line has been opened to the public in disconnected segments as the Enola Low Grade Trail. Amtrak upgraded the surface to a crushed-stone trail concurrently with its transmission line replacement project. The first portion of the trail opened in September 2011. In late spring and early summer 2017, Martic and Conestoga townships resurfaced their portions of the trail. In July 2017, construction began on a pedestrian bridge for the trail over U.S. Route 222 north of Quarryville, with completion expected in April 2018. Improvement on the portion of the trail in Eden, Bart, and Sadsbury townships is expected to begin in 2019. The Safe Harbor Trestle remains closed as of 2017.
