View of the interior of the exit cone of the Variable-Density Tunnel (VDT) during its brief period of operation as an open throat design. After the fire, the VDT section engineers decided to convert the tunnel to an open throat design. Operations of the redesigned tunnel began in April 1928, however the engineers could not succeed in getting the new tunnel to operate properly and decided to return to the original closed throat design. The tunnel began closed throat operations in December 1930.
