Elevator Round-Trip Time, Interval, and Handling Capacity

Architect, and tenant improvement eventually asks for. Round-trip time is the sum of three things and knowing their relative sizes is most of the insight. The TRAVEL term is the round trip at rated speed. The STOPPING term is the number of stops the car probably makes times what each stop costs -- door open, dwell, close, accelerate, decelerate -- and on a typical office run it is the LARGEST of the three. The TRANSFER term is passengers boarding and alighting. Because stopping dominates, faster cars help far less than people expect: a car that spends 41 seconds travelling and 80 seconds stopping barely improves with a higher rated speed, and doubling the rated speed on a 150 second round trip takes only 21 seconds off it. It gets better with faster doors, shorter dwell, and above all fewer stops, which is exactly what zoning a tall building into low-rise and high-rise banks accomplishes. Two outputs matter and they measure different things. INTERVAL is the average wait and it is what a tenant notices: under about 30 seconds is good office service and over 40 generates complaints. HANDLING CAPACITY is throughput in the five-minute peak as a percentage of the building population, and 12 to 15 percent is the conventional office target. A ten-story building with 120 ft of rise, three cars at 350 fpm carrying 12 people past 7 probable stops passes on capacity at 14.4 percent and fails badly on interval at 50 seconds -- it can move the people, it just makes them wait to do it, and meeting a 30 second interval takes five cars rather than three. A single-zone up-peak analysis using assumed probable stops, which is the classical hand method and not what a modern consultant uses: real analysis simulates the traffic, computes probable stops from the population distribution, handles down-peak and interfloor traffic, and models destination dispatch, which changes the answer substantially. ASME A17.1, the elevator consultant, and the AHJ govern.

RTT = 2 x rise / (speed/60) + (probable stops + 1) x stop time + 2 x passengers x transfer time; interval = RTT / cars; handling capacity per car = 300 x passengers / RTT; total = that x cars; percent = total / population x 100; cars for a target interval = ceil(RTT / target).

The classical elevator round-trip-time up-peak traffic analysis (travel at rated speed, probable stops times time per stop, and passenger transfer time), with interval and five-minute handling capacity following from it, cited by name. The conventional office targets -- interval under about 30 s, handling capacity 12% to 15% of population -- are stated as design practice, not reproduced from any table. A hand method, not a traffic study: ASME A17.1, the elevator consultant, and the AHJ govern.

The round-trip-time relation is public and stated in full; the probable-stops figure, the stop time, and the transfer time are the user's own building-and-equipment values.

Estimate. AHJ and licensed professional govern.

Field names used by the API: rise_ft, car_speed_fpm, passengers_per_trip, probable_stops, stop_time_s, transfer_time_s, cars, population, target_interval_s, travel_s, stopping_s, transfer_s, rtt_s, interval_s, hc_per_car, hc_total, hc_percent, cars_for_target

• Stopping dominates on a typical office run the stopping term exceeds both travel and transfer; fewer stops, not a faster car, is the leverelevator traffic analysis practice
• Conventional targets interval under about 30 s is good office service; handling capacity 12% to 15% of populationelevator traffic analysis practice
• Up-peak, single zone assumed probable stops; down-peak, interfloor, and destination dispatch are not modeledelevator traffic analysis practice