VISSIM 5.30-05 User Manual

7 Simulation of Pedestrians
number of user-defined routes, but with the dynamic potential, they implicitly
select their route out of a continuous, infinite and uncountable set of potential
trajectories.
7.1.8.9 Dynamic Potential: Use Cases
Compared with travel time based partial routes and partial routes in general,
there are many use cases, which in principle could be addressed either with
the dynamic potential or using partial routes, and the difference in the degree
of how these are suited also can be large or small, i.e. in one case – after
some experience with both – it is obvious that partial routes are the method
of choice, in another only the dynamic potential can lead to the expected
behavior, in a third group success might come with either method and a
fourth group contains those cases to which neither the partial routes nor the
dynamic potentials can so far successfully be applied.
There is a rule of thumb which method probably would be the better one to
be used. As partial routes are discrete and the dynamic potential is
continuous in many aspects, one at first think of partial routes to model
situations of discrete choice and the dynamic potential to model continuous
choices. The simplest examples are probably the flow of a large group of
pedestrians around a 90° or 180° corner to be modelled with the dynamic
potential but to use partial routes, when in the corner there is an array of
ticket gates which discretizes the choice set. “In the corner” here implies that
the path length from origin to destination is different for each ticket gate.
Nevertheless, as the editing effort for the dynamic potential usually is much
smaller than for partial routes, one might sometimes try to model situations
with the dynamic potential which appear to be better suited for partial routes.
For that reason it is intended to offer a refined dynamic potential method in
future VISSIM versions, which extends its scope of application into what
currently is the realm of partial routes.
7.1.8.10 Dynamic Potential: Editing
Follow the steps outlined below to define the dynamic potential:
► Activate a route such that it is shown with all red, blue and green dots
and the yellow line.
► Press the ALT key while double-clicking on a destination point (green or
blue).
The Routing Point window appears, cf. section 7.1.8.11.
► Activate the option Use Dynamic Potential.
► Set the Impact which describes the strength of influence.
- If the value is 1% the method is activated and calculation time for it is
consumed (as much as for any other parameter choice), but it almost
has no effect and the pedestrians continue to desire to walk on the
shortest path.
388 VISSIM 5.30-05 © PTV AG 2011