The Switch-Back Gravity Railroad was completed in 1827 to transport coal from Summit Hill to Mauch Chunk and on to the Lehigh Canal for delivery to points south. For almost 20 years this was a one way trip from Summit Hill to Mauch Chunk and soon proved to be a problem. Empty cars had to wait for the full cars, thus creating a bottle-neck in Mauch Chunk. A return track, or back-track, from Mauch Chunk to Summit Hill was completed in 1845.
Some interesting photos as well.