VISSIM 5.30-05 User Manual

5 Base Data for Simulation
5.2 Distributions
A range of parameters in VISSIM is defined as a distribution rather than a
fixed value. Thus the stochastic nature of traffic situations is reflected
realistically. Most of the distributions are handled similarly and it is possible
to use any kind of empirical or stochastic data for definition. All distributions
can be accessed by BASE DATA - DISTRIBUTIONS.
5.2.1 Desired Speed Distribution
For any vehicle type the speed distribution is an important parameter that
has a significant influence on roadway capacity and achievable travel
speeds. If not hindered by other vehicles, a driver will travel at his desired
speed (with a small stochastic variation called oscillation). The more vehicles
differ in their desired speed, the more platoons are created. If overtaking is
possible, any vehicle with a higher desired speed than its current travel
speed is checking for the opportunity to pass - without endangering other
vehicles, of course.
Stochastic distributions of desired speeds are defined for each vehicle type
within each vehicle composition. The window Desired Speed Distribution can
be accessed via BASE DATA – DISTRIBUTIONS - DESIRED SPEED.... A desired
speed distribution can then be selected (single mouse click), edited (single
mouse click and EDIT or double click) or created (NEW). Creating or editing a
desired speed distribution opens the window shown above.
The minimum and maximum values for the desired speed distribution are to
be entered into the two fields above the graph (the left number must always
110 VISSIM 5.30-05 © PTV AG 2011