Designated dangerous cargo may be handled, loaded, discharged, or transported at any designated waterfront facility only if a permit therefor has been issued by the Captain of the Port. This permit requirement may be waived, at the discretion of the Captain of the Port, when such cargoes are contained within railroad cars or highway vehicles which are moved on or across a waterfront facility used primarily for the transfer of railroad cars or highway vehicles to or from a railroad or highway vehicle ferry or carfloat; provided such designated cargoes are not removed from, or placed in, the railroad car or highway vehicle while it is in or on such waterfront facility.