Pedestrians' big debut in traffic simulation - PTV America

Multi-modal traffic simulation
with realistic interaction
numbers. Sooner or later, most traffic engineers will
have to tell the city council what their plans are. A film
can communicate their vision much more impressively
than a bunch of numbers. Visualizing traffic planning
results for laypeople and decision makers is a major
feature of our software,“ said Vortisch.
If, for example, a city is planning to install a traffic-
calming measure to make a square more pedestrianfriendly,
the program allows users to determine the
impact on traffic and initiate the required construction.
In this context, it is important to not only provide
urban planners with the appropriate information, but
also to make such information understandable for
members of the community in order to involve them
in the further development of their life space.
How it all began –
insights into the development
When PTV decided to integrate pedestrian simulation
in its product family, it began looking for a partner in
academia. Peter Vortisch explains why the company
contacted Dirk Helbing from the Swiss Federal Institute
of Technology in Zurich. “Helbing has been working
on the social force model for pedestrian dynamics for
years. When we looked for a research partner, we
wanted a model that would complement our own
methodical approach and be as microscopic as possible.
The social force model is ideal because it continuously
looks at the space and thus allows you to represent
reality in a realistic fashion.“
The PTV experts involved potential users throughout the
entire development process. The software was developed
in close consultation with users in the field so that
it would contain precisely the components they needed.
VISSIM has always modelled pedestrians, but there
was only a greatly simplified behavioural model for
them. It was used, for example, to simulate the obstacles
for motorists turning right. However, it was not
possible to model pedestrian behaviour in correct
quantities.
“In order to embed pedestrians in VISSIM, we had to
not only add another behavioural model, but also enhance
the simulation mechanics and handling,“ said
Vortisch. “The decisive factor is that pedestrians move
on a plane and not linearly like vehicles. Vehicles are
bound by lanes. Pedestrians move around freely on a
plane, and can walk to the side or back. What‘s more,
they can stop and speed up with hardly any loss of
time. That means we now have to look at a new element
which is orientated towards planes and not lanes.
We have therefore significantly expanded the user interface
to model the pedestrian infrastructure as well.“
The driving force – the social force model
Dirk Helbing and Peter Molnar developed the social
force model in 1995. Pedestrians‘ movements are modelled
by different forces based on Newtonian concepts.
This includes the driving force, which causes
pedestrians to generally move towards a certain target,
i.e., walk towards their destination at a certain pace.
However, they are influenced by different elements.
First, people keep a sort of “safety distance“ from other
pedestrians and from obstacles or buildings. Second, different
attractions – such as shop windows, for example
– distract them so that they change their path. There
are thus psychological (social force) and physical factors
that are taken into account during modelling.
How the new pedestrian
simulation in VISSIM
came about
TRAFFIC
COMPASS INTERNATIONAL 01/2008 07