VISSIM 5.30-05 User Manual

12 Dynamic Assignment
average of the coordinates. (You can see the computed zone centroids in the
network editor by using default shortcut CTRL+Z while in mode Parking Lot).
The coefficients of the utility
function can be defined for each
vehicle type in the Parking Lot
Selection window. The window is
reached by pressing the button
PARKING LOT SELECTION in the
[SPECIAL] tab page of the Vehicle
Type window.
Once the utility for all valid parking lots in the choice set is determined, the
choice probabilities are computed by a Logit function. The sensitivity factor of
the parking lot Logit model can be set in the Dynamic Assignment window in
the field labeled Logit Scaling Factor. There is also a field labeled Logit
Lower Limit, where a threshold can be defined, so that parking lots with a
utility less than the threshold are not chosen at all.
12.7.3 Detour Detection
As described above in the section about route search, the vehicles are
encouraged to find new routes by trying links that are not yet traveled. This
may lead to useless routes in the route collection. A route is considered
useless if it is an obvious detour, and we define an obvious detour as a route
that can be generated out of an other known route by replacing a sequence
of links by a much longer sequence (in terms of distance). How much longer
the replacing link sequence must be to qualify as a detour can be defined by
the user in the Dynamic Assignment window. E.g. if there is a detour factor of
2 defined then all routes are checked whether they are just copies of other
routes with a subroute replaced by another partial route that is at least
double as long.
If detour detection is active you can choose in the path visualization window
whether you want to see the detected detours or the non-detour routes.
12.7.4 Correction of Overlapping Paths
For every OD pair the whole demand will be distributed on all available
routes. The distribution considers the general cost values as defined by the
decision parameters of the route choice model. A route is assembled by a
sequence of edges. Two routes are different if their sequence of edges is not
exactly the same. Therefore two routes may be considered different if they
632 VISSIM 5.30-05 © PTV AG 2011