Baltimore and Ohio 4500 is a 2-8-2 "USRA Light Mikado" steam locomotive built by the Baldwin Locomotive Works in Philadelphia, Pennsylvania in July 1918 for the Baltimore and Ohio Railroad (B&O) as a member of the Q-3 class. The locomotive hauled freight for the B&O until retirement in August 1957 and was donated for display at the B&O Railroad Museum in Baltimore, Maryland. It is the sole surviving Baltimore and Ohio Mikado type steam locomotive.