VT Planner uses calculation and simulation workflows to help teams compare elevator alternatives under explicit assumptions. This note explains how three common calculation metrics relate to each other and where simulation adds more context.
Why these metrics matter
Elevator traffic analysis often starts with a sizing question: can a group of elevators serve the expected demand within a reasonable service target? RTT, interval, and handling capacity help answer that question in a structured way, especially for classic up-peak or early design checks.
They are not the whole service picture. A system can have acceptable capacity indicators while still producing uncomfortable waiting times, long queues, or poor tail-percentile experiences in a dynamic scenario.
What is RTT?
RTT, or Round Trip Time, is the time for an elevator car to complete a representative service cycle and return to the main terminal or reference point. In a classic up-peak calculation, RTT is one of the main quantities used to understand how quickly the group can complete repeated passenger service cycles.
RTT depends on assumptions such as building height, probable stops, door timing, passenger transfer time, car speed, acceleration, and the selected traffic model. It is useful because it connects physical elevator behavior with group capacity.
How interval relates to RTT
Interval is the average time between successive elevator services at the main terminal or reference point. In the simplified up-peak relationship, the group interval is derived from RTT and the number of elevators in the group.
That makes interval a compact way to compare alternatives. If RTT goes down or the number of cars goes up, interval can improve. If RTT increases because stops, travel, or door times increase, interval usually worsens.
What handling capacity means
Handling capacity describes how many passengers an elevator system can sustainably transport in a defined period under specified traffic and loading assumptions. In elevator traffic studies it is often discussed as a five-minute capacity measure.
In the classic up-peak chain, RTT is used to derive interval, and interval is then used to estimate handling capacity. This is why the three metrics should be read together rather than as isolated numbers.
Why handling capacity is not enough
Handling capacity is a capacity metric, not a complete passenger experience metric. It should not be confused with rated car capacity or treated as proof of good service. A group can show a capacity result that looks acceptable while queues, waiting time, or journey time still become unacceptable in a more complex scenario.
For that reason, capacity metrics should be reviewed alongside passenger experience metrics such as average waiting time, journey time, queue length, completion rate, and p90 or p95 percentiles.
Where simulation adds value
Analytical calculation is useful for early sizing and for understanding the main capacity drivers. Simulation becomes more useful when the project includes mixed traffic, multiple entrances, zoning, transfer floors, destination dispatch, non-uniform population, near-capacity conditions, or questions about passenger experience.
In those cases, the result is not only about RTT, interval, or handling capacity. The decision also depends on how passengers arrive, queue, board, transfer, wait, and complete their trips over time.
How VT Planner uses the metrics
VT Planner lets teams compare calculation and simulation results under saved building and elevator setup assumptions. Reports can include calculation metrics, simulation metrics, run history, charts, and the assumptions behind each result.
This helps keep capacity checks, passenger service metrics, and alternative comparison in the same project record. The analysis documentation explains how teams run studies, and results and reports covers how outputs are reviewed.
A practical reading order
- Use RTT to understand the cycle mechanics behind the group.
- Use interval to compare how often service is available under the assumptions.
- Use handling capacity to understand passenger throughput under a defined traffic condition.
- Use waiting time, journey time, queues, and percentiles to understand passenger experience.
- Use simulation when dynamic behavior and variability matter to the decision.
Want to compare elevator capacity metrics with simulation results and report-ready outputs?
Start Free Trial Back to VT Planner Read about simulation software Open technical glossary View sample report