Transportation Systems Simulation - A Tutorial for Multi-Modal Simulation Using VISSIM/Traffic Data Input

Vehicle volume data is needed for certain links or network entry-points. These links include the first entrance link for the freeway mainlines and on-ramps. The data used in the following example is 5 minute loop detector data over a 3 hour period.

Data Collection

PeMS

5 minute loop detector data is used to accurately simulate vehicle flow dynamics. The vehicle volume data is provided by the Caltrans Performance Measurement System (PeMS) website http://pems.dot.ca.gov/ (see Figure below).

Vehicle Parameters

Vehicle Composition

Vehicle composition determines the percentage of cars and trucks (HGV). There are many ways to collect vehicle composition data. One way is manually count the number of passenger cars and trucks from a video recording, Aerial photos or using Google Maps. Data for Annual Average Daily Truck Traffic on California State Highways can be found at http://traffic-counts.dot.ca.gov/.

1. From the top toolbar, Select Traffic > Vehicle Composition
2. A window will appear below the Network Editor (see Figure below)
3. From the dropdown menu, Select “Relative Flow”, the window will split into two sections
4. Input the different types of vehicles as a percentage or an absolute value under the column “RelFlow”
   

Percentage:0.85 (85%) Car and 0.15 (15%) HGV – Heavy Goods Vehicle (Trucks)

Or

Absolute Val: 170 Car and 30 HGV

Desired Speed Distribution

1. Next to the “RelFlow” column is the Desired Speed Distribution (DesSpeedDistr) for each vehicle type
   • VISSIM only displays speeds in kilometers per hour (km/h)
2. Use Google to quickly find the miles per hour (mph) equivalent (see Figures below)
   • Use Google Map’s Street View to identify the speed limit of your highway segment
3. Select the miles per hour equivalent for each vehicle type
   • Example: 100 kmph = 62 mph

TIP: Cars in free flow conditions generally travel 5 mph over the posted speed limit. Trucks on average travel close to the posted speed limit. Exact speeds and distributions can be designated by selecting “New…” from the dropdown list. A new window will appear. Name the new Speed Distribution and input the minimum and maximum miles per hour (see Figure below).

Vehicle Data

Time Intervals

Before we input vehicle volumes, we need to first define our time intervals. Since we collected 5-min loop detector data from PeMS, each interval is 300 seconds. For every hour there are 12 intervals of 300 seconds therefore 3 hours of data is 36 intervals.

1. Select Base Data > Time Intervals in the toolbar. A “Time Intervals” window will appear below the Network Editor (see Figure below)
2. Select the “Vehicle Inputs” from the dropdown list
3. Right Click on an empty area. Select “Add…”
4. Change the Start value of the second line to 300
5. Right Click on an empty area. Select “Add…” repeatedly until you have 36 rows (Count:36)
6. The last row should have a start value of 10500.
7. Select “Vehicle routes (static)” from the dropdown list
8. Repeat steps 2-5

TIP: A new time interval can be quickly added by Right Clicking and then pressing “A” key.

Vehicle Inputs

Input the time-dependent traffic demand data and adjust for realistic vehicular behavior. The key metric for vehicle input is volume or the number of vehicles in a given time frame. Volume data can be found on the Excel spreadsheet previously created from the PeMS database.

VISSIM: (see Figure below)

1. Click on the “Vehicle Inputs” under Network Objects
2. Locate the entrance of your desired link, this is where the vehicles will start their journey on the network
3. Select Vehicle Inputs under Network Objects
4. Right Click on the link and select “Add New Vehicle Input” or CTRL+ Right Click
5. A black line will appear across all lanes at the beginning of the link
6. Double Click on the black line, the “Vehicle Inputs” window will appear below the Network Editor
7. Select “Vehicle volumes by time interval” from the dropdown list, the window will split into two sections

Excel: (see Figure below)

1. Open the Excel spreadsheet that contains the 5-min loop data from the PeMS website
2. Locate the appropriate “Timestamp” and “Station ID”
3. Select the 36 cells under the “Total Flow” column
4. Press CTRL+C on your keyboard to copy the exact number of vehicle volume intervals/cells (36)

VISSIM:

1. In the right section of the “Vehicle Inputs” window locate and Click on the first row
2. Press CTRL+V to paste the volumes from Excel
3. Change the “VolType” for all rows to “Exact”
4. Repeat steps 1-13 for every unique entry point (On-Ramps) in your network
5. The final version should look similar to the Figure below

TIP: Make sure that the 5-min volumes from the Excel spreadsheet have been converted to “per hour” by multiplying the entire “Total Flow” column by 12. Excel allows columns to be filtered by a specific criteria. Select the top cell of any column and press CTRL+SHIFT+L. A small “down arrow” will appear next to every column header. This option might help you quickly find the appropriate StationID.

Vehicle Routes

At any diverging point or off-ramp, we must determine the turning percentage or Relative Volumes (RelFlow).

VISSIM:

1. Click on the “Vehicle Routes (Static)” under Network Objects (see Figures below)
2. Locate the entrance of your desired link, this is where the vehicles will start their journey on the network
3. Select Vehicle Routes (Static) under Network Objects
4. Right Click on the link and select “Add New Static Vehicle Routing Decision” or CTRL+ Right Click
5. A pink line will appear across all lanes and a blue (teal) line will follow your cursor
6. The yellow path connecting the pink and teal lines is the Vehicle Route
7. Move your cursor along the highway until you reach the very end of the first Off-Ramp
8. Left Click on the Off-Ramp to define you first Vehicle Route
9. Move your cursor on the mainline (highway) somewhere slightly past the first Off-Ramp
10. Left Click on the Mainline to define you second Vehicle Route
11. Double Click anywhere off the highway network links to finalize your choices
12. Double Click on the pink line of your Vehicle Route,
    • The “Static Vehicle Routing Decision” window will appear below the Network Editor
13. Select the “Static vehicle routes” from the dropdown list, the Network Editor will split into two sections
14. In the left section, select the Vehicle Route group (row 1) created in the previous steps
15. The right section displays the two Vehicle Routes choices
16. In the right section, Click on the first row or the row with the Off-Ramp as the “DestLink”

Excel: (see Figure below)

1. Open the Excel spreadsheet that contains the 5-min loop data from the PeMS website
2. Locate the appropriate “Timestamp” and “Station ID” of the first Off-Ramp
3. Select the 36 cells under the “Total Flow” column for the Off-Ramp
4. Transpose the data to appear horizontal
5. Press CTRL+C on your keyboard to copy the total vehicle counts (volume)

VISSIM:

1. In VISSIM, locate the “RelFlow(0)” cell for the Off-Ramp in the right section of the “Static Vehicle Routes” window
2. Press CTRL+V to paste the volumes from Excel
3. In the right section below the Network Editor, Click on the second row or the row with the Mainline (ML) as the “DestLink”

Excel:

1. Open the Excel spreadsheet that contains the 5-min loop data from the PeMS website
2. Locate the appropriate “Timestamp” and “Station ID” of the ML (Mainline)
3. Select the 36 cells under the “Total Flow” column for the Mainline
4. Transpose the data to appear horizontal
5. Press CTRL+C to copy the total vehicle counts (volume)

VISSIM:

1. In VISSIM, locate the “RelFlow(0)” cell for the ML in the right section of the “Static Vehicle Routes” window
2. Press CTRL+V to paste the volumes from Excel
3. Repeat steps 1-30 if your highway network has multiple off-ramps
4. The final version should look similar the Figure below

TIP: Introducing multiple “Vehicle Routes” either at the entrance of on-ramps or in middle of the highway Mainline can increase the accuracy of the final simulation. This technique may require tinkering.

Data Collection Points

Loop detectors (Stations) are added in VISSIM to collect data such as vehicle counts and speed. Before adding data collection points in VISSIM, Google Maps can be used to locate each Station’s approximate location. Locate every loop detector using Google Map’s Street View. Mainline loops are often upstream (before) and after (downstream) from Off-Ramps and On-Ramps (see Figure below).

VISSIM:

1. Select “Data Collection Points” under Network Objects
2. Move the cursor over the exact location and lane
3. Right Click and select “Add new Data Collection Point” (Shortcut: CTRL+Right Click)
   • Once placed, the Collection Points can be moved by dragging them around with your mouse
   • They can also be deleted by selecting each or multiple (CTRL + Click) Collection Points and pressing Delete
4. Add every Data Collection Point for every lane at each loop detector location for your entire Network
5. Double Click any Collection Point to make a window appear below the Network Editor called “Data Collection Point”
6. Name every Collection Point with its corresponding SationID (see Figure below)

1. On the top toolbar, Select List > Measurement > Data Collection Measurements
2. A new window will appear below the Network Editor called “Data Collection Measurements”
3. In an empty area of the new window, Right Click and select “Generate all (grouped)”
4. From the top toolbar, select Evaluation > Configuration
5. In the new “Evaluation Configuration” window Select the “Result Management” Tab
   • Select “of all simulation runs”
   • Uncheck the “Automatically add new columns in lists”
   • Select “File”
6. Select the “Result Attributes” Tab
   • Check the box for “Data collections” under the “Collect data” column
   • From time = 0
   • To time = 10800
   • Interval = 300
7. Click OK (see Figures below)

1. From the top toolbar, select Simulation > Parameters
2. In the new “Simulation Parameters” window Change the “Period:” to 10800
3. Click OK (see Figure below)

1. Select the “Data Collection Measurements” tab below the “Network Editor”
2. Click the “Select attributes” button (the black wrench)
3. In top left corner of the new window, Click the “Filter…” button
4. In the new “Preselection Filter” window, under “Simulation Runs”…
   • Select “Show only selected simulation runs”
   • Check: Current run
5. Under “Interval Times”…
   • Select “Show only selected time intervals”
   • Check: Last Completed
   • Check: Total
   • Check: Average
   • Check All: from “0-300” to “10500-10800”
6. Under “Vehicle Classes”…
   • Select “Show only selected vehicle classes”
   • Check: All type
7. Click OK

TIP: Use the Figure below as a guide. If your group is only analyzing two hours, then time intervals will only extent to “6900-7200”.

1. Back in the “Data Collection Measurement: Select Attributes” window, Click on the “Vehicles” attribute
2. Click on the “Green Arrow” to add every vehicle attribute for all time intervals to the right hand section of the window
3. Click OK (see Figure below)
4. Now in the “Data Collection” tab below the Network Editor, each Collection Point group will have every time interval as a column

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