VISSIM 5.30-05 User Manual

Driving Behavior
● The number of Observed vehicles affects how well vehicles in the
network can predict other vehicles´ movements and react accordingly. As
some of the network elements are internally modeled as vehicles it might
be useful to increase this value if there are several cross sections of
network elements within a short distance. However, the simulation will
run slower with higher values.
● The Look back distance defines the distance that a vehicle can see backwards
in order to react to other vehicles behind (within the same link).
- The min. value is important when modeling lateral vehicle behavior.
Especially if several vehicles can queue next to each other (e.g.
bikes) this value needs to be increased. The value depends on the
approach speed. In urban areas it could be 20-30m (60-100 ft).
- The max. value is the maximum distance allowed for looking
backward. In networks with many small meshes, e.g. with many
connectors over a short distance, the simulation speed can be
improved if the maximum look back distance is reduced from the
default value.
● Temporary lack of attention (“sleep” parameter): Vehicles will not react to
a preceding vehicle (except for emergency braking) for a certain amount
of time.
- Duration defines how long this lack of attention lasts.
- Probability defines how often this lack of attention occurs.
The higher both of these parameters are, the lower the capacity on the
corresponding links will be.
● Car following model selects the basic model for the vehicle following
behavior. Depending on the selected model the Model parameters
change.
- Wiedemann 74: Model mainly suitable for urban traffic
- Wiedemann 99: Model mainly suitable for interurban (motorway)
traffic
- No Interaction: Vehicles do not recognize any other vehicles (can be
used for a simplified pedestrian behavior).
● Model parameters: Depending on the selected Car following model a
different number of Model parameters is available. Cf. sections 5.4.2.1
and 5.4.2.2 for details.
These are the main parameters to affect the saturation flow rate. For
examples, cf. section 5.4.6.
5.4.2.1 Wiedemann 74 Model Parameters
This model is an improved version of Wiedemann’s 1974 car following
model. The following parameters are available:
● Average standstill distance (ax) defines the average desired distance
between stopped cars. It has a variation between -1.0 m and +1.0 m
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