VISSIM 5.30-05 User Manual

8 Simulation and Test
The larger the time intervals between the communications between the
operational and the supervising level the more the simulation on the
operational level can develop into a wrong direction.
For the simulation of vehicles one can typically allow for a bit larger time
steps than for the simulation of pedestrians as for pedestrians in their two
spatial dimensions there are more possibilities (degrees of freedom) to
run astray. The possibility to choose 1 simulation step per second
therefore can be fine for a vehicles-only simulation. It can also be fine
during the building process of a model including pedestrians, but once
problems occur and for the evaluation and measurement 5 or 10
simulation steps per second should be set if pedestrians are included in
the model.
The interaction between vehicles is subject to changes when changing the
time steps value and thus the simulation results can be different. Thus we
strongly recommend not to change this parameter during a simulation run
or even during a running project.
The simulation resolution also controls the playback speed of *.AVI files
recorded with VISSIM. Please take note of this dependency when choosing
the simulation resolution for a new project.
If pedestrians are included in the simulation, the Simulation Resolution
value is not subject to changes during the simulation run.
● Random Seed: This parameter initializes the random number generator.
Simulation runs with identical input files and random seeds generate
identical results. Using a different random seed changes the profile of the
traffic arriving and therefore results may also change. In this way, the
stochastic variation of input flow arrival times can be simulated. For
meaningful results it is recommended to determine the arithmetic mean
based on the results of multiple simulation runs with different random
seed settings.
When using multiple simulation runs with different random seeds, the
option Generate exact number of vehicles is to be switched on for all input
flows in the network.
Instead of running multiple simulation runs with different random seeds, a
multirun simulation can be started via SIMULATION - MULTIRUN, cf. section
8.1.3.
● Simulation Speed: The number of simulation seconds to a real time
second. If maximum is selected, the simulation will run as fast as
possible. The change of the Simulation Speed does not affect the results
of the simulation and can therefore be done at any time during the
simulation.
Note: The achieved actual simulation speed depends on the size of the
network to be simulated and the computer hardware used.
452 VISSIM 5.30-05 © PTV AG 2011