Transcript Introduction to VISSIM - Oregon Institute of Technology

Introduction to VISSIM
Oregon Institute of Technology
Traffic Engineering Laboratory
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VISSIM
 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
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VISSIM
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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)
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What is VISSIM?
 VISSIM consists internally of three different parts:
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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
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Model Interaction
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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
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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.
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Traffic Flow Model
 The basic idea of the Wiedemann model is
the assumption that a driver can be in one of
four driving modes:
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Free driving
Approaching
Following
Braking
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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.
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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.
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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.
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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.
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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.
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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.
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?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.
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Car following model
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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)
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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.
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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
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Beyond car following…
 Attributes characterizing each driver vehicle-
unit can be discriminated into three
categories:
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Vehicle specifications
Driver-vehicle behavior
Interaction among vehicles
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Beyond car following…
 Technical specifications of the vehicle, e.g.
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Length
Maximum speed
Potential acceleration
Actual position in the network
Actual speed and acceleration
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Beyond car following…
 Behavior of driver-vehicle-unit, e.g.
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Psycho-physical sensitivity thresholds of the
driver (ability to estimate, aggressiveness)
Memory of driver
Acceleration based on current speed and
driver’s desired speed
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Beyond car following…
 Interdependence of driver-vehicle-units, e.g.
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Reference to leading and following vehicles on
own and adjacent travel lanes
Reference to current link and next intersection
Reference to next traffic signal
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