Strategies for serving peak elevator traffic

Suppose that in an office building of moderate height (5 to 20 floors) elevator traffic during peak periods is predominantly between a lobby floor and various upper floors. We compare the waiting plus riding time and the average number of passengers carried per trip for various strategies. In particular, if two (or more) elevators serve the same group of floors (a common strategy), the waiting plus riding time would typically be (slightly) less if one split the group into two parts and had each elevator serve separate parts of this group. The latter strategy would have considerably fewer passengers per trip. It may also be advantageous to have a single elevator serve different floors on successive trips. Seldom would it be advantageous for an elevator to serve more than 2 or 3 floors on any trip. If elevator systems used more efficient strategies during peak periods, buildings would not need as many elevators.