It would make more sense to say "one" to me though.
It's like a waitress saying, "one cheeseburger with fries, coming up". It's like Hudson is serving up one express elevator to hell..
I always felt that Hudson was goofing around and pretending to be an elevator valet. A valet would say something like one express elevator, going down, rather than we're on an express elevator because that would be stating the obvious..