## I have run the same simulation for 5 minutes, 15 minutes, and an hour. Why do I get different results?

Elevate simulations start with the elevators empty at the home floor. Naturally, the first passengers will experience waiting times that are shorter than if all the cars were busy serving other passengers. In a 5 minute simulation, this "head start" can significantly bias the results, usually resulting in an optimistic estimate of performance. When you simulate for longer periods, the effect of this starting condition is much reduced.

If you are running a situation where traffic is heavier than the system can sustain, then the longer you run the simulation, the worse the queues will be, and thus the reported performance is worse. In this case, you might want to experiment with the inputs. You might change the inputs so that your system will not be overloaded (e.g., change the speed of the elevators or even the number of elevators ). Or you might wish to study how long after the last simulated passenger has entered the system before the system returns to equilibrium.

Also note that with longer periods, there is more chance of their being variations in intensity within the period. e.g. if you have a period with 10 persons per 5 minutes for 15 minutes then in the first 5 minutes there may be 12 people, second 7 people, and third 11 people. If the system is running close to saturation, it may fall behind in the first 5 minutes, and then never catch up. As a consequence, three 5 minute periods may give better results than one 15 minute period.

So how long a time should you run a simulation? The simple answer is to run a simulation for a long enough time so that the results are independent of the starting conditions. Elevate defaults to a single 15 minute period because in the "real world", most traffic peaks are rarely sustained for longer than this.  An alternative to using the same traffic intensity for a 15 minute simulation is to use Elevate’s Advanced Passenger Data feature to model the traffic changes over a period of time.  Or use one of the preset traffic profiles available, and described in the Elevate manual.  Then you can use Elevate's results graphs to review how the traffic has changed in intensity over time, and how this has impacted on waiting times, queues, etc.