2 ELEVATORS SERVING UP-TRAFFIC

A model is described for the motion of two elevators serving traffic o nly from a single lobby floor to multiple higher floors. Over a certai n range of passenger arrival rates, the average round trip time of an elevator can be approximated by a linear function of the number of pas sengers carried which, in rum, is proportional to the time since the l ast elevator departure from the lobby (the headway). A pair of determi nistic equations for the means of two state variables describes the ap proximate evolution of the system behavior. These equations lead to a very strange chaotic type of motion in the two-dimensional state space . For moderately light traffic the two elevators lend to travel close together, but for heavy traffic the headways tend to be nearly uniform ly distributed over the mean round trip time of a single elevator.