Up peak is a mode designed for situations where the majority of the demand for the elevator(s) is upwards (for example an office building at the start of a workday). In up peak, all elevators will be parked with their doors open on a specified floor (usually a lobby). When people have gotten into the elevator and selected their floors, the elevator will then go to those floors as usual, however once it has reached the highest floor called it will go back to the lobby and repeat these actions.
During Up Peak mode (also called Moderate Incoming Traffic), elevator cars in a group are recalled to the lobby to provide expeditious service to passengers arriving at the building, most typically in the morning as people arrive for work or at the conclusion of a lunch-time period.
Elevators are dispatched one-by-one when they reach a pre-determined passenger load, or when they have had their doors opened for a certain period of time. The next elevator to be dispatched usually has its hall lantern or a "this car leaving next" sign illuminated, to encourage passengers to make maximum use of the available elevator system capacity.
The commencement of Up Peak may be triggered by a time clock, by the departure of a certain number of fully loaded cars leaving the lobby within a given time period, or by a switch manually operated by a building attendant.