Skylobby

A sky lobby is an intermediate interchange floor where people can change from an express elevator that stops only at the sky lobby to a local elevator which stops at every floor within a segment of the building. When designing very tall (supertall) buildings, supplying enough elevators is a problem – travellers wanting to reach a specific higher floor may conceivably have to stop at a very large number of other floors on the way up to let other passengers off and on. This increases travel time, and indirectly requires many more elevator shafts to still allow acceptable travel times – thus reducing effective floor space on each floor for all levels. The other main technique to increase usage without adding more elevator shafts is double-deck elevators.

Early uses of the sky lobby include the original Twin Towers of the World Trade Center and the John Hancock Center in Chicago.

The John Hancock Center's sky lobby on the 44th floor serves only the residential portion of the building that occupies floors 45–92. Three express elevators run from the residential lobby on the ground floor to the 44th floor, with two of the elevators stopping at the parking garage's main level on floor 6. At floor 44, residents transfer to two banks of three elevators. One bank serves floors 45–65 and the other serves 65–92. Although all six elevators stop at floor 65, this floor is roughly the same layout as the residential floors immediately above and below it. It is not a sky lobby because residents can also board elevators to higher floors at floor 44.

The Hancock's 44th floor sky lobby includes a pool, gym, dry cleaner, convenience store, about 700 mailboxes, two "party" rooms, a sitting area overlooking Lake Michigan, a small library, a refuse room (with trash chutes emptying here), offices for the managers of the residential condominium, and a polling station for residents during elections.

Floors above 92 are serviced by direct passenger elevators from the ground floor, by an emergency elevator from the ground floor, and by two freight elevators that run from floors 44 to 98.

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Wikipedia