VISSIM 5.30-05 User Manual

6 The Traffic Network
Filter
option
Additionally, the Routes section provides option Show only routes over link:
► Check this option and
► Select one of the VISSIM network links from the list.
Then only those routes will be listed in the Routes section which traverse
this link. Simultaneously, they will be highlighted in the network display.
6.4.4.6 How Routing Decisions Come Into Action
Routes
in general
Partial
Routes
During the simulation each vehicle that passes a routing decision point is
assigned a specific route unless it already has a route assigned to it. The
stochastic distribution onto multiple routes at a single routing decision point
is based on a Monte Carlo methodology; in other words the percentage of
vehicles on each route corresponds directly to the routes’ designated
relative flow volume. A vehicle that is assigned to a specific route chooses
its travel lane on multiple lane roadways independently so that it can reach
the next connector along its route. As soon as it reaches a certain range
defined as Lane change parameter of the next downstream connector that
is included in its route, it tries to change to a lane that leads to this
connector. From this point the vehicle will not change to a lane not leading
to the connector for the purpose of passing a slower vehicle except when it
approaches a PT vehicle that stops.
In the 2D mode, a lane change is indicated by a short red bar at the front of
the vehicle (indicator) and in the 3D model as a flashing indicator (if it is
defined in the 3D model).
Vehicles on the destination travel lane of the indicating vehicle will cooperate
in allowing the vehicle to change lanes according to their driving
behavior parameters (cf. section 5.4.3).
A routing decision needs to be placed well in advance of the point where
the routes divide into different directions. This is to allow the vehicle to react
to its new destination. In addition, for multi-lane links it is to avoid unrealistic
queues due to the fact that at a routing decision all vehicles will get routing
information and thus more weaving might appear in the simulation than in
reality. As a rule-of-thumb, the routing decision should be placed further upstream
than the longest queue expected on that link (but - of course -
downstream of the end of all previous routes).
For example, partial routes can be used to model route diversion caused by
variable message signs (VMS) without the need to change each individual
route that passes the section where the VMS is active. Instead simply one
partial routing decision with two routes (if there are two alternative routes
possible) and the desired proportions of traffic assigned to these partial
routes need to be defined.
Recommended placement
When a sequence of routing decisions is used (e.g. modeling turning movements
for each junction separately) it is important to remember that a vehicle
232 VISSIM 5.30-05 © PTV AG 2011