Hier eine Erklärung mit den Links zu den Plänen, um das ohne viel Suchen nachzuvollziehen.
One point should be adressed: due to misleading phrasing in NIST-reports (though NIST makes this false statement so often, that I have problems in believing that this isn't done deliberateley), many people think that there were more than three continuing shafts. Read again from the above NIST-quote:
* Those going to floors 44 through 74 took one of eight express elevators to the 44th floor skylobby before transferring to one of 24 local elevators, These 24 were stacked on top of the of the lower bank of 24, providing additional transport without increasing the occupied floor space.
* Those going to floors 78 through 107 took one of 10 express elevators from the Concourse Level to the 78th floor before transferring to one of 24 local elevators. These were also stacked on the lower banks of 24.
The concept of multiple elevators within a common shaft was first used in the WTC towers and has since become the norm for buildings taller than about 50 stories.
(NIST NCSTAR1-1, p.9 - PDF)
This gives the impression that different elevators shared the same shaft, because they were stacked on top of each other to save floor space. Though it does not even seem to be technically possible, people often bring this point in to prove that there were more than three continuing shafts.
To make an end to this false assumptions, we only have to look at the floor plans.
The key point to observe from what NIST says is, “providing additional transport without increasing floor space”. The elevators were stacked, as in, local elevators would keep the in the same path throughout the building. For example, as per the NIST report, below shows the variations in floor plans as each bank of local elevators terminate, giving the higher levels more floor space.
All four banks occupying floor space.
Bank A terminates, giving these levels more floor space.
Bank B terminates, giving these levels more floor space.
Bank C terminates, giving these levels more floor space.
Here is the 42nd floor upper mechanical room, bank D terminates to allow for the motor to be intalled over the shaft.
Here is the bank D elevator elevation drawing. Note that the shaft terminates and does not continue past the mechanical room. If we look at the top of the drawing we can see that the mechanical room is sealed by the 43rd floor. The drawing shows above this area on the 43rd floor are toilets and a new zone 2 elevator shaft pit. Hence the elevators are stacked.
Here we have the 43rd floor showing the postion of the toilets and the new zone 2 elevator shaft pits.
Here is the 44th floor lobby starting off again. Notice the local elevators are in the same positions, hence they are “stacked”.