Elevator Traffic Interval
Calculate the traffic interval (average waiting time) of an elevator group, INT = RTT ÷ N, dividing the round trip time RTT (s) by the number of elevators N in the group. The result, in seconds, is the average time between elevator arrivals at the main floor — the main service-quality indicator perceived by users (waiting time). Intervals up to 30 s are excellent; above 50-60 s, poor. More elevators in the group reduce the interval. It is the key criterion in sizing the number of elevators. Enter the RTT and the number of elevators.
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Traffic interval
The traffic interval is what the user actually feels: the average waiting time for an elevator. For a group of N elevators working together, INT = RTT ÷ N, the round-trip time divided by the number of cars. The logic: if one car completes a cycle every RTT seconds, and N of them are evenly spread around that cycle, a car reaches the lobby every RTT/N seconds — that is the mean headway between arrivals, and hence the average wait (the worst-case wait is the interval itself; the perceived average, about half of it). The interval is the main quality-of-service indicator of an elevator system, with well-established bands: intervals up to ~30 s count as excellent (prime office buildings); 30-40 s, good; 40-50 s, fair; above 50-60 s, poor (users grow impatient, complain, take the stairs). It is the decisive criterion when sizing the number of elevators: cars are added to the group until the interval drops into the band acceptable for the building use. There is an economic trade-off — more elevators improve service but cost dearly (shaft, machines, prime floor area lost). Modern destination dispatch algorithms (the user keys the floor into a hall panel) group passengers and cut the RTT, improving the interval without adding cars. Enter the RTT and the number of elevators.
Related Tools
Number of Elevators Required
Calculate the number of elevators required, N = peak demand ÷ capacity per elevator, dividing the peak transport demand (people in 5 min) by the handling capacity of a single elevator (people in 5 min). The result is the minimum number of elevators in the group to meet peak demand. In practice, round up and also check the resulting traffic interval (waiting quality). Peak demand comes from the building population times the peak percentage (12-15% in offices). Undersizing causes queues and long waits. Enter the peak demand and the capacity per elevator.
Round Trip Time (RTT)
Estimate an elevator's round trip time (RTT), RTT = 2·(H ÷ v) + stops × t_stop, from the travel height H (m), the speed v (m/s), the number of probable stops and the average time per stop (s, including deceleration, door opening/closing and boarding). The result, in seconds, is the time of a complete up-and-down cycle with stops — a central parameter of vertical traffic analysis. The higher the RTT, the lower the handling capacity and the longer the interval between cars. Enter the height, the speed, the number of stops and the time per stop.
Handling Capacity (5 min)
Calculate an elevator's handling capacity over 5 minutes, HC = (300 × Q) ÷ RTT, from the car capacity Q (people) and the round trip time RTT (s). The result, in people carried per 5 minutes, is the standard vertical-traffic performance metric (building peak demand is usually measured over 5 min). The factor 300 is the seconds in 5 minutes. Multiplied by the number of elevators and compared with the building population, it tells whether the system meets demand (typically 12-15% of the population in 5 min in offices). Enter the car capacity and the RTT.
Building Population
Estimate a building's population, Pop = (area per floor × number of floors) ÷ density, from the usable area per floor (m²), the number of floors and the occupancy density (m² per person). The result, in people, is the total population to be served by the vertical transport — the starting point of elevator traffic analysis. Occupancy density varies with use: ~10 m²/person in dense offices, ~15-20 m²/person in standard offices, with specific values for hotels and residences. Compared with the elevators' handling capacity, it tells whether the system is adequate. Enter the area per floor, the number of floors and the density.
Probable Stops
Calculate the probable number of stops of an elevator, S = N × (1 − (1 − 1/N)^P), from the number of served floors N and the number of passengers P in the car. The result is how many floors, on average, the elevator actually stops at during a trip (probabilistically, two passengers may go to the same floor). It is an essential parameter of the round trip time calculation: more stops raise the RTT. The formula assumes passengers choose destination floors randomly and uniformly. With a full car, S approaches N (stops at almost all). Enter the number of floors and passengers.
Elevator Motor Power
Calculate the motor power of an elevator, P = m·g·v ÷ η, from the payload m (kg), gravity g (9.81 m/s²), nominal speed v (m/s) and the system efficiency η (motor, gearbox, sheaves). The result, in watts, is the mechanical power needed to hoist the load at nominal speed. In practice, the counterweight (balancing the car plus ~45% of the load) reduces the effective power, and regenerative braking on descent can return some to the system. It is the base calculation for sizing the traction machine. Enter the load, the speed and the efficiency.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.