Vissim-Training.doc

VISSIM GUIDE

INTRODUCTORY TRAINING VISSIM VISSIM is a microscopic, time step and behavior based simulation model developed to model urban traffic and public transit operations. The

program

can

analyze

traffic

and

transit

operations

under

constraints such as lane configuration, traffic composition, traffic signals, transit stops, etc., thus making it a useful tool for the evaluation of various alternatives based on transportation engineering and planning measures of effectiveness. The traffic simulator in VISSIM is a microscopic traffic flow simulation model including the car following and lane change 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.

•

Open VISSIM and create a new file

For every transport network a separate VISSIM file is needed. To create a new network the following steps are to be followed. 1.

Open the master plan of your study area as a background image

Building an accurate VISSIM model at least one scaled map that shows the real network. The image file of a digitized map (.jpg, .tiff, .bmp etc.) is to be imported as a background. This background can be displayed, moved and scaled in the VISSIM network window and is used to trace the VISSIM links and connectors. 2.

Scale the background and save a scaled background.

Precise scaling is necessary for an accurate network model. A large scale distance (> 100 m / > 300 ft) is recommended to use. 3.

Draw links and connectors for streets and junctions

The level of detail required for replicating the modeled transport network

infrastructure

depends

on

the

purpose

of

a

VISSIM

application. While a rough outline of the analyzed intersection is sufficient for testing traffic actuated signal logic, a more detailed model is required for simulation analyses. Link: The first step in coding a VISSIM network is to trace links. Each approach and section should be represented by one link. A link cannot

have multiple sections with a different number of lanes. Connectors (rather than links) should be used to model turning movements. Connectors:

In order to create a road network, links need to be

connected to other links. It is not sufficient to place one link on top of another link in order for vehicles to continue on the other link. Instead, a connector needs to be created to connect the two links. Furthermore connectors are used to model turnings of junctions.

• 1.

Set Parameters for the new file Simulation Parameters

Traffic regulations: Specifies the standard driving side (For Ireland, Leftside-Traffic). Simulation Resolution: The number of times the vehicle’s position will be calculated within one simulated second (range 1 to 10) (more than 3 recommended). Random

Seed:

This

parameter

initializes

the

random

number

generator. Simulation runs with identical input files and random seeds generate identical results. Using a different random seed includes a stochastic variation of input flow arrival times.

2.

Speed profiles

Some parameters in VISSIM are defined as a distribution rather than a fixed value. Thus the stochastic nature of traffic situations is reflected realistically. Most of the distributions are handled similarly and it is possible to use any kind of empirical or stochastic data for definition. Stochastic distributions of desired speeds are defined for each vehicle type within each traffic composition. The minimum and maximum values for the desired speed distribution are to be entered along with two intermediate points are generally adequate to define an s-shaped distribution. 3.

Vehicle Acceleration and Deceleration Functions

VISSIM does not use a single acceleration and deceleration value but uses functions to represent the differences in a driver’s behavior. Acceleration and deceleration are functions of the current speed. These functions are predefined for each of the default vehicle types in VISSIM. They can be edited or new graphs can be created

4.

Dwell Time Distribution (Stops & Parking Lots)

The dwell time distribution is used by VISSIM for dwell times at parking lots, stop signs, toll counters or transit stops. Either a normal distribution or an empirical distribution can be provided for transit stops. 5.

Vehicle type characteristics

In addition to the default vehicle types (Car, HGV, Bus, Tram, Bike and Pedestrian), new vehicle types can be created or existing types modified. A vehicle class represents a logical container for one or more previously defined vehicle types.

6.

Create traffic compositions

A traffic composition defines the vehicle mix of each input flow to be defined for the VISSIM network. The relative percentage (proportion) of each vehicle type is to be given. 7.

Enter traffic volumes at network endpoints and pedestrian

volumes at junctions In VISSIM, time variable traffic volumes to enter the network can be defined. For vehicle input definition, at least one traffic composition has to be defined. Traffic volumes are defined for each link and each time interval in vehicles per hour. Within one time interval vehicles enter the link based on a Poisson distribution.

• 1.

Fine Tuning of the VISSIM Network

Enter routing decision points and associated routes

A route is a fixed sequence of links and connectors. A route starts from a routing decision point (red cross-section) and extends up to at least one destination point (green cross-section) or multiple destinations. A route can have any length - from a turning movement at a single

junction to a route that stretches throughout the entire VISSIM network. For static routing decisions, vehicles from a start point (red) to any of the defined destinations (green) using a static percentage for each destination. 2. Enter speed changes Reduced speed areas:

When modeling short sections of slow speed

characteristics (e.g. curves or bends), the use of reduced speed areas is advantageous over the use of desired speed decisions. In order for a reduced speed area to become effective vehicles need to pass its start position. Desired Speed Decisions:

A desired speed decision is to be placed

at a location where a permanent speed change should become effective. The typical application is the location of a speed sign in reality. 3.

Enter priority rules

Priority rules are to be applied for non-signalized intersections, permissive left turns, right turns on red light and pedestrian crosswalks.

The

right-of-way

for

non-signal-protected

conflicting

movements is modeled with priority rules. This applies to all situations where vehicles on different links/connectors should recognize each other. The two main conditions to check at the conflict marker(s) are minimum headway (distance) and minimum gap time. Conflict areas are a new alternative to priority rules to define priority in intersections. They are the recommended solution in most cases

because they are more easily defined and the resulting vehicle behavior is more intelligent. A conflict area can be defined wherever two links/connectors in the VISSIM network overlap. For each conflict area, the user can select which of the conflicting links has right of way (if any). 4.

Enter stop signs

Intersection approaches controlled by STOP signs are modeled in VISSIM as a combination of priority rule and STOP sign. A STOP sign forces vehicles to stop for at least one time step regardless of the presence of conflicting traffic while the priority rule deals with conflicting traffic, looking for minimum gap time and headway etc. STOP signs are required to be installed for non-signalized intersections and for right turns on red light.

•

Create Signal Controls

Signalized intersections can be modeled in VISSIM either using the built-in

fixed-time

control

or an optional external

signal

state

generator. (Our license in Trinity has a fixed time control.) In VISSIM every signal controller (SC) is represented by its individual SC number and signal phase. Signal indications are typically updated at the end of each simulation second. Signal control and signal groups are to be modeled from Signal Control window. In Fixed Time Signal Control VISSIM starts a signal cycle at second 1 and ends with second Cycle time.

•

Setup for output files and run simulations

 travel time segments Using Travel Time Measurements mode, a section of the network has to be selected on which the travel time is to be measured. The

output

format

can

be

configured

according

to

the

requirement of the user.  delay segments Based on travel time sections VISSIM can generate delay data for networks. A delay segment is based on one or more travel time sections. All vehicles that pass these travel time sections are captured by the delay segment. A delay time measurement determines - compared to the ideal travel time (no other vehicles, no signal control) - the mean time delay calculated from all vehicles observed on a single or several link sections.  queue counters The queue counter feature in VISSIM provides as output the average queue length, maximum queue length and the number of vehicle stops within the queue. Queues are counted from the location of the queue counter on the link or connector upstream to the final vehicle that is in queue condition. If the queue backs up onto multiple different approaches the queue counter will record information for all of them and report the longest as the maximum queue length.  data collection points

Data collection offers the collection of data on single cross sections.

QUICKSTART CHECKLIST 1. Open VISSIM and create a new file 2. Set the simulation parameters 3. Create/edit speed profiles 4. Check/edit vehicle type characteristics 5. Create traffic compositions 6. Open the master plan of your study area as a background image 7. Place and scale the background image and save background image file. 8. Draw links and connectors for roadways tracks and crosswalks 9. Enter traffic volumes at network endpoints and pedestrian volumes at junctions 10. Enter routing decision points and associated routes 11. Enter speed changes 12. Enter priority rules for non-signalized intersections 13. Enter stop signs for non-signalized intersections 14. Create Signal Controls with signal groups 15. Enter signal heads in network 16. Enter detectors for intersections controlled by traffic actuated signal control 17. Enter stop signs for right turns on red 18. Enter priority rules 19. Create dwell time distributions and place transit stops in network 20. Create transit lines 21. Setup for output files 22. Run the simulation