In the mid-1980s, the tunnel's original length of 1.4 miles or 7340 feet was extended an additional three-tenths of a mile (480 m) further south of its original Camden Station portal when the B&O successor CSX Transportation's mainline track east of the B&O warehouse was covered over for construction of Interstate 395 (ref: Stephen J. Salamon, David P. Oroszi, and David P. Ori, Baltimore and Ohio – Reflections of the Capitol Dome.