Elevator Traffic Analysis Calculator (Handling Capacity & Interval)
Up-peak elevator traffic analysis: round-trip time, five-minute handling capacity, interval, average waiting and transit time and the number of cars needed for an office, residential, hotel or hospital building — from population or floor area, floors, floor height, car size, speed, door times and an express zone.
How it works
CC = car capacity ÷ 75 kg; P = CC × load factor · S = N(1 − (1 − 1/N)^P) · H = N − Σ(i/N)^P · tv = floor height ÷ speed · tf(1) = single-floor flight time (+ start delay) · ts = tf(1) − tv + door time · RTT = 2H·tv + (S + 1)·ts + 2P·tp (+ 2 × express run) · interval = RTT ÷ cars · HC5 = 300·P·cars ÷ RTT · AWT ≈ (0.4 + (1.8·P/CC − 0.77)²) × interval · ATT ≈ 0.5·H·tv + 0.5·S·ts + P·tp
Elevator traffic design uses the classic up-peak round-trip calculation (Barney and Strakosch, CIBSE Guide D, ISO 8100-32): assume each car fills at the lobby to about 80% of its rated persons, estimate how many floors it will probably stop at (S) and how high it will probably go (H) for that many passengers, and add the travel time at rated speed, the time lost at every stop for slowing, levelling, door cycles and starting again, and the time for people to step in and out. The round-trip time divided by the number of cars is the interval between departures from the lobby, and the passengers moved per round trip scaled to five minutes, as a share of the population, is the handling capacity. Waiting time is estimated from the interval and how full the cars are, and transit time from half a round trip. Targets depend on the building: offices aim for 12–15% in five minutes with 25–30 s intervals, hotels and hospitals accept 30–50 s, and apartments 40–60 s with 5–8%. The tables show what one more car or a larger car would do, and why tall buildings are split into zones served by express elevators: probable stops, not speed, dominate the round trip.
Worked example
A 600-person, 10-floor office (3.9 m floors) with three 1,000 kg cars at 1.6 m/s: a 1,000 kg car is rated for 13 persons and carries 10 at 80% loading. Each trip probably makes 6.5 stops with a reversal at floor 9.5. Travel takes 2 × 9.5 × 2.44 = 46 s, the 7.5 stops cost 7.5 × 7 = 53 s and 20 passenger movements 24 s, a round-trip time near 123 s. The interval is 41 s, far longer than the 30 s an office should have, while the five-minute handling capacity of 12.2% is just good; average waiting time is about 32 s. A fourth car brings the interval to about 31 s.
Sources: Elevator World — Fundamentals of Traffic Analysis (up-peak RTT, ISO 8100-32 criteria) · Peters Research — Elevate RTT calculation results · CIBSE Guide D: Transportation systems in buildings
Frequently asked questions
Why 75 kg per person and 80% loading?
EN 81 and ISO 8100 rate cars at 75 kg per person; in practice people stop boarding at about 80% of nominal capacity because of shoulder room and bags, so a 1,000 kg (13-person) car carries around 10 at peak.
How many elevators does an office building need?
Enough to move 12–15% of the population in five minutes with an interval of about 30 s or less. As a guide, a 10-floor building of 600 people usually needs three or four 1,000 kg cars; the Cars needed line and the number-of-cars table work it out for your building.
What is the difference between interval and waiting time?
The interval is the average time between cars leaving the lobby. Passengers arrive at random, so they wait less than a full interval: at 50% car loading about 0.4 of the interval, rising to about 0.85 of it at 80% loading, because full cars leave people behind.
How do destination-dispatch systems change this?
Grouping passengers by destination cuts the probable stops per trip, typically raising handling capacity by 15–30% for the same cars; the calculation here assumes conventional collective control, so it is on the safe side.
When do I need a zoned building or express elevators?
When the round trip gets too long to meet the interval with a reasonable number of cars — usually beyond about 15–20 floors. Split the floors into low, mid and high zones, each with its own group; for an upper zone, enter its floors and the floors passed non-stop as express floors.
Related calculators
Standard material-handling and site-safety arithmetic (OSHA 1926/1910, ASME B30, manufacturer data-plate conventions). The equipment's own load chart, data plate and a competent person's site assessment govern; never exceed rated capacity.