Tuscarora Creek (Monocacy River) bridge - Credit: Wikimedia Commons
The Tuscarora Creek bridge is a single-span, steel, through-girder bridge with a floor beam/stringer system supporting a 12-inch-thick concrete slab south of Walkersville, Maryland. Originally constructed by the Frederick and Pennsylvania Line Railroad Company (F&PL) in 1872. It was later rebuilt by the Pennsylvania Railroad in 1907 as a thru girder concrete deck bridge using an older bridge from the Northern Central Railway. In 1915, the bridge was surveyed as part of the Interstate Commerce Commission's effort to establish freight rates for the Parent railroad. Read more on Wikipedia
Source: en.wikipedia.org