The calculated time for a single elevator car to depart from the main terminal floor, serve all probable stops on a journey up and down, and return to the main terminal floor ready for the next trip.
Full Definition
Round Trip Time (RTT) is the cornerstone calculation in elevator traffic design, used to determine how many cars are required in a group to achieve acceptable waiting intervals. RTT = T_departure + T_flight_up + T_stops_up + T_door_cycles + T_flight_down + T_stops_down + T_return. Each component is calculated from rated speed, acceleration/deceleration profile, door opening/closing time, passenger transfer time (typically 1.2–1.5 s per person boarding/alighting), and the probable number of stops (calculated probabilistically from building population and number of floors). A shorter RTT means fewer cars are needed, or conversely better service from the same number of cars. Destination dispatch systems reduce RTT by grouping passengers travelling to the same floor, reducing the number of intermediate stops. CIBSE Guide D Appendix A provides the full RTT formula.
