Excellent question. You may have to ask on theit official forums for an answer. I don't know if this has ever been addresses in the regular media (interviews, articles and such), I certainly haven't heard anything one way or the other.
Of course you won't be able to...why do so many people ask this question? How many games can you honestly say have ever been able to do this? I'm sure any figure you throw at me will be able to fit one hand. --- "Only the badasses should use the elevator" account of a survivor during a zombie apocalypse