High Quality Content by WIKIPEDIA articles! The Baltimore Belt Line was constructed by the Baltimore and Ohio Railroad (B&O) in the 1890s to connect the railroad`s newly constructed line to Philadelphia (with trackage rights to New York City) with the rest of the railroad at Baltimore, Maryland. It included the Howard Street Tunnel, the Mount Royal Station 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.