1. Introduction to VISSIM
Oregon Institute of Technology
Traffic Engineering Laboratory

2. V I S S I M
The name is derived from the German words “Verkehr In Städten - SIMulationsmodell”
Approximate translation =
Traffic in cities - simulation model
Produced by PTV Planung Transport Verkehr, Karlsruhe, Germany

3. V I S S I M

4. What is VISSIM?
VISSIM is a microscopic, time step, and behavior based traffic simulation computer program
VISSIM models urban traffic and public transit operations
VISSIM can analyze traffic (cars, trucks, pedestrians) and transit (buses, trains, trams) operations under constraints such as lane configuration, traffic composition, traffic signals, transit stops, etc.
VISSIM has robust pedestrian modeling capabilities (particularly in V5.1)

5. What is VISSIM? VISSIM consists internally of three different parts:
Traffic flow model
Traffic control (signal light) model
Data analysis package
The traffic flow model generates an online visualization of traffic operations
The traffic control model generates the indications (i.e. green, red, amber) which is “exported” to the traffic flow model
The data analysis package creates offline output files containing statistical data such as travel times and queue lengths

6. Model Interaction

7. Traffic Flow Model
Developed by Rainer Wiedemann in 1974 at Karlsruhe University, updated 1999
Car-following model that considers physical and psychological aspects of the drivers

8. Traffic Flow Model
Discrete, stochastic, time step based, microscopic model with driver-vehicle-units as single entities.
Contains a psycho-physical car following model for longitudinal vehicle movement and a rule-based algorithm for lateral movements.

9. Traffic Flow Model
The basic idea of the Wiedemann model is the assumption that a driver can be in one of four driving modes:
Free driving
Approaching
Following
Braking

10. Free Driving No influence of preceding vehicles observable
The driver seeks to reach and maintain a certain speed, her individually desired speed.
In real life, and in VISSIM, the speed in free driving cannot be kept constant, but oscillates around the desired speed due to imperfect throttle control.

11. Approaching
The process of adapting the driver’s own speed to the lower speed of a preceding vehicle.
While approaching, a driver applies a deceleration so that the speed difference of the two vehicles is zero in the moment he reaches his desired safety distance.

12. Following
The driver follows the preceding car without any conscious acceleration or deceleration.
He keeps the safety distance more or less constant, but again due to imperfect throttle control and imperfect estimation the speed difference oscillates around zero.

13. Braking
The application of medium to high deceleration rates if the distance falls below the desired safety distance.
This can happen if the preceding car changes speed abruptly, of if a third car changes lanes in front of the observed driver.

14. Traffic Flow Model
For each mode, the acceleration is described as a result of speed, speed difference, distance and the individual characteristics of driver and vehicle.
The driver switches from one mode to another as soon as he reaches a certain threshold that can be expressed as a combination of speed difference and distance.

15. Traffic Flow Model
For example, a small speed difference can only be realized in small distances, whereas large speed differences force approaching drivers to react much earlier.
The ability to perceive speed differences and to estimate distances varies among the driver population, as well as the desired speeds and safety distances.

16. ?Psycho-Physical?
Because of the combination of psychological aspects and physiological restrictions of the driver’s perception, the model is called a psycho-physical car-following model.

17. Car following model

18. How does a 1974 model simulate 2009 drivers?
The model has been calibrated through multiple field measurements at the Technical University of Karlsruhe, Germany.
Periodical field measurements and their resulting updates of model parameters ensure that changes in driver behavior and vehicle improvements are accounted for.
Latest revisions in early 2009 (V 5.1)

19. Beyond car following…
VISSIM’s traffic simulator not only allows drivers on multiple lane roadways to react to preceding vehicles (2 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.

20. Beyond car following…
VISSIM simulates the traffic flow by moving “driver-vehicle-units” through a network.
Every driver with his specific behavior characteristics is assigned to a vehicle with its own characteristics.
As a consequence, the driver’s behavior corresponds to the technical capabilities of his vehicle

21. Beyond car following…
Attributes characterizing each driver vehicle- unit can be discriminated into three categories:
Vehicle specifications
Driver-vehicle behavior
Interaction among vehicles

22. Beyond car following… Technical specifications of the vehicle, e.g.
Length
Maximum speed
Potential acceleration
Actual position in the network
Actual speed and acceleration

23. Beyond car following… Behavior of driver-vehicle-unit, e.g.
Psycho-physical sensitivity thresholds of the driver (ability to estimate, aggressiveness)
Memory of driver
Acceleration based on current speed and driver’s desired speed

24. Beyond car following… Interdependence of driver-vehicle-units, e.g.
Reference to leading and following vehicles on own and adjacent travel lanes
Reference to current link and next intersection
Reference to next traffic signal