The Baltimore Belt Line was constructed by the Baltimore and Ohio Railroad (B&O) in the early 1890s to connect the railroad's newly constructed line to Philadelphia and New York City/Jersey City with the rest of the railroad at Baltimore, Maryland. It included the Howard Street Tunnel, the Mount Royal Station for B&O's Royal Blue Line passenger trains, and the first mainline railroad electrification in the United States. The line is currently operated by CSX Transportation as part of its Baltimore Terminal Subdivision.