PTV Vissim- Speed Definition

Before adding desired speed distributions, it is important to check whether the network is using the preferred units. Go to “Base Data > Network Settings” and select “Units” tab. You can either select different units for each data type (i.e. Length, Speed, Acceleration) or click on the “All Imperial” or “All Metric” button. These will update unit settings for all types of data automatically.

You can access the list of desired speed distributions by going to “Base Data > Distributions > Desired Speed”.  Then, the “Desired Speed  Distributions” window will be loaded. The window might contain a list of existing desired speed distributions which are already defined in the model.

On the desired speed distributions window, first, look for the configuration buttons on the top of the list. Click the green add button to create a new distribution or click the red remove button to delete an existing distribution or click the edit button to modify or view an existing distribution.

As stated above, click the green add button or right click inside the desired speed distributions window to create a new distribution. This will open the “Desired Speed Distribution” window, where you will need to define:

• Distribution Number
• Distribution Name
• Minimum Desired Speed
• Maximum Desired Speed

You can define your own desired speed distribution by using the “Distribution Graph” field within the “Desired Speed Distribution” window.

1) Define Minimum and Maximum speed that you would like to use.

2) Move mouse cursor along the straight line with the graph.

3) “Right click” on the line and make sure a data point (red-dot) is added along the line.

4) “Left click” and “hold” on a data point (red-dot) to grab it and move around within the graph.

5) Check the data values shown on both the x-axis (desired speed point) and y-axis (probability of selected desired speed point) and move to the appropriate position.

6) Add data points (red-dots) as needed by following the steps above.

7) If you need to remove data point(s):

• “Left click” and “hold” data point and move to the “right top corner” or “left bottom corner” or
• “Left click” and “hold” data point and move to the adjacent data point.                                 

8) Create all desired speed distributions that you will need to use before adding speed objects to the model.

Note: “Name” attribute is just a text field which will not be updated even if you change the “unit” setting. If you would like to check whether your unit setting is appropriate, check “Network Settings” and the data points defined for each desired speed distribution.

Desired speed distributions defined by following the steps above can be applied to each vehicle 1) when they enter the network and 2) while they are traveling throughout the network. Each vehicle will be assigned values for the following attributes:

• Desired Speed Distribution
• Desired Speed Fractile

Vehicle composition data can be used for the “Vehicle inputs” object.

Vehicle composition data can be accessed by going to “Traffic > Vehicle Compositions”. Then, the “Vehicle Compositions” list will be loaded, which will contain a list of existing vehicle compositions that are already defined in the model.

On the vehicle compositions window, look for the configuration buttons on the top of the window. Click the green add button to create a new vehicle composition or click the red remove button to delete an existing vehicle composition or click the edit button to modify or view an existing vehicle composition.

As stated above, click the green add button or right-click inside the vehicle compositions window to create a new vehicle composition, which will add a new data row to the window. Click on the “Relation List” dropdown box and select “Relative flows”. It will load another data table on the right-side displaying details on each vehicle composition. On this window, you will need to check and define:

• Vehicle Type
• Desired Speed Distribution
• Relative Flow

Vehicle Type

The list of vehicle types that will be used for the composition.

Desired Speed Distribution

Desired speed distribution selected for each vehicle type.

Relative Flow

Relative share of the vehicle type in the composition. The scale of this data can be anything (i.e. 30% or 0.3 or 300 vehicles); however, it has to be made sure that the scale is used consistently because the sum of all relative flows always forms the basis of 100% and the absolute shares are calculated based on that.

“Public Transport Line” is used to model network entry points as well as routing throughout the network for public transport vehicles. Once a public transport line is added, you can specify desired speed distributions that each public transport vehicle will be using upon entrance.

In the case of dynamic assignment in PTV Vissim, the parking lot object is used as a zone connector to load traffic onto the network. As a part of the details, you can specify the desired speed distribution for each vehicle class entering the network through the given parking lot.

Each vehicle is assigned a fractile value when it enters the network. This fractile value will be used to assign the corresponding speed value from the desired speed distribution, as a vehicle passes through desired speed decision points or reduced speed areas. This value will remain unchanged for the vehicle during the entire simulation run and is stored within the “Desired Speed Fractile” attribute.

For example, if the fractile value is 65% as shown in the figure below, the vehicle will always be assigned the 65^th percentile value of the desired speed distribution. If this value is 100%, the vehicle will always be assigned the highest value in the desired speed distribution.

As described in the earlier section, vehicles are generated with a pre-determined desired speed. After entering the network, you can use the following two objects to update the desired speed distributions assigned to each vehicle:

• Desired Speed Decision Point
• Reduced Speed Area

Even though both objects are used to update desired speed data for vehicles, there are differences between these two objects. A detailed comparison can be found in the section below.

Like numerous other objects in PTV Vissim (i.e., signal head, stop sign, data collection point, etc.), a desired speed decision is a bar that can be placed at a point for each lane. If a desired speed update needs to happen across multiple lanes, you will need to place desired speed decisions on each lane. On the other hand, reduced speed areas are an area object. These are defined by drawing a box along the link and similar to desired speed decisions, they will need to be defined for each lane.

As shown in the figure below, once a vehicle passes through a desired speed decision, the desired speed data for the vehicle gets permanently updated until it passes through another desired speed decision. Conceptually, it acts like posted speed limit signs. When a vehicle passes a desired speed decision their desired speed changes to the posted speed on the desired speed decision point.

On the contrary, a reduced speed area temporarily updates the vehicle’s speed while it travels within the area. Once the vehicle has exited the area, the vehicle will return to its original desired speed as shown in the figure below.

To create a new desired speed decision point in a lane, follow the steps below:

1) Click the “Desired Speed Decisions” in the network objects window to be in desired speed decision points insert mode.

2) Zoom in to the location where the new desired speed decision point will be placed.

3) Left click to select the link or connector where the desired speed decision point will be placed.

4) Move mouse cursor to the selected lane and press <CTRL> + Right click to place the desired speed decision point. The “Desired Speed Decision” window will open.

5) Define the following data for the desired speed decision point:

Vehicle Class

Vehicle classes for which the desired speed decision applies. Different desired speed distributions can be applied to different vehicle classes.

Desired Speed Distribution

The desired speed distribution that will be applied to the specified vehicle class. This will be the new speed once the vehicle passes through the desired speed decision.

6) Click the “OK” button to save the settings.

To create a new reduced speed area on a link (or connector) follow the steps below:

1) Click the “Reduced Speed Area” in the network objects window to be in reduced speed area insert mode.

2) Zoom into the link (or connector) where the reduced speed area will be placed and “Left-click” to select the link. (If you need to check background map (or image), switch to wireframe model by pressing <CTRL> + A.)

3) Move the mouse cursor to the location on the link where the reduced speed area should start.

4) Press “<CTRL> + Right click” and “hold”; then, “drag” it along the link toward the direction of travel.

5) Release all keys and buttons and the new reduced speed area will be added to the selected link.

6) When the “Reduced Speed Area” window is open, enter the following data:

Vehicle Class

Vehicle classes for which the reduced speed area applies. Different desired speed distributions can be applied to different vehicle classes as needed.

Desired Speed Distribution

The desired speed distribution that will be applied to the specified vehicle class. This will be the new speed while the vehicle is within the reduced speed area.

Deceleration Rate

The maximum deceleration used for faster vehicles as they approach the reduced speed area. The lower this value is, the further away a vehicle will begin to reduce its speed.

7) Click the “OK” button to save the settings.