VISSIM 5.30-05 User Manual

1 Introduction
Car following logic (Wiedemann 1974)
The accuracy of a traffic simulation model is mainly dependent on the quality
of the vehicle modeling, e.g. the methodology of moving vehicles through the
network. In contrast to less complex models using constant speeds and
deterministic car following logic, VISSIM uses the psycho-physical driver
behavior model developed by WIEDEMANN (1974). The basic concept of
this model is that the driver of a faster moving vehicle starts to decelerate as
he reaches his individual perception threshold to a slower moving vehicle.
Since he cannot exactly determine the speed of that vehicle, his speed will
fall below that vehicle’s speed until he starts to slightly accelerate again after
reaching another perception threshold. This results in an iterative process of
acceleration and deceleration.
Stochastic distributions of speed and spacing thresholds replicate individual
driver behavior characteristics. The model has been calibrated through
multiple field measurements at the Technical University of Karlsruhe (since
2009 KIT – Karlsruher Institut für Technologie), Germany. Periodical field
measurements and their resulting updates of model parameters ensure that
changes in driver behavior and vehicle improvements are accounted for.
VISSIM’s traffic simulator not only allows drivers on multiple lane roadways
to react to preceding vehicles (4 by default), but also neighboring vehicles on
the adjacent travel lanes are taken into account. Furthermore, approaching a
traffic signal results in a higher alertness for drivers at a distance of 100
meters in front of the stop line.
VISSIM simulates the traffic flow by moving “driver-vehicle-units” through a
network. Every driver with his specific behavior characteristics is assigned to
a specific vehicle. As a consequence, the driving behavior corresponds to
24 VISSIM 5.30-05 © PTV AG 2011