The 18th street railroad bridge is actually 2 bridges. One is called the Saint Charles Air Line Bridge. This is currently owned by the CN railroad. It is the southern most of the two bridges. It was originally 260 feet in length. It was built in 1919. It was designed to be modified when the Chicago River straightening project was completed.
The bridge was was designed by the Strauss Bascule Bridge Company. It was fabricated by the American Bridge Company. It was a double track structure. It was assembled in its original location by the Ferro Construction Company. The original substructure was built by the Foundation Company of New York.
When the river straightening project was completed, the bridge was moved and shortened in 1930. E.J. Albrecht Company built the relocation substructure. The Stroebel Steel Construction Company dismantled and and re-erected the superstructure in its location. The bridge was shortened to 220 feet. This bridge is still operational.
The adjacent bridge was commissioned by the Baltimore and Ohio Railroad. It was constructed by the American Bridge Company. It contained two tracks. It is a single leaf Strauss trunnion bascule bridge. It measures 186 feet in length. Its supports are concrete.