Adjusting Driving Behavior

 

After the first simulation, your group may have encountered unusual behavior. VISSIM v7 has tools to adjust a few driving parameters. Every link and connector can have a unique Behavior Type. Under “Network Objects” Right Click “Links” and Select “Show List”. A new window will appear below the network editor. All Links and Connectors by default should be “Urban (motorized)” as the “LinkBehavType”.

TIP: VISSIM uses two types of models: Wiedemann 74 and Wiedemann 99.
Wiedemann 74 is suitable for urban traffic and merging areas.
Wiedemann 99 is suitable freeway traffic with no merging areas.
You may need to change the “LinkBehavType” for some or all links/connectors.
WARNING: Run the simulation first with default values. Only make the following adjustments if the first simulation does not accurately represent highway traffic behavior.
 
 

Wiedemann Model (Following)

  1. To adjust specific parameters for each Wiedemann model, Select Base Data > Driving Behaviors from the top toolbar (see Figure below)

  2. A new “Driving Behavior” window will appear below the Network Editor

  3. Right Click your desired CarFollowModType and select “Edit…”

  4.  A new window will appear and only adjust the following parameters

  • "Following” tab and Car following model: Wiedemann 74

    • Look ahead distance

    • Look back distance

    • Average standstill distance                                                                                          

 
 

 

  • “Following” tab and Car following model: Wiedemann 99 (see Figure below) 

    • Look ahead distance

    • Look back distance

    • CC0 (Standstill Distance)

    • CC1 (Headway Time)

    • CC2 (‘Following’ Variation)

 
 
TIP: Only change parameter values in small increments if necessary. The Table below shows the default value and the Suggested Range for each parameter.
 
 

CC0 (Standstill Distance): the average desired standstill distance between two vehicles or the desired rear-bumper to front-bumper distance (feet) between stopped vehicles, as shown in the Figure below.

 
 

CC1 (Headway Time): is the gap (seconds) which a driver wants to maintain at a certain speed. The higher the value, the more cautious the driver is as shown in the Figure below. Desired Safety Distance = CC1 +CCO.

 
 

CC2 (Following Variation): is the longitudinal oscillation during following conditions. It defines the additional distance (feet) from the desired safety distance a driver allows before he intentionally moves closer to the car in front. (See Figure below)

 
 

Wiedemann Model (Lane Change)

  • “Lane Change” tab and General behavior: “Free lane selection” or “Slow lane rule”

  • Check the “Cooperative lane change” box (see Figure below)

 
 

  • The posted speed limit is not representative of the average speed of vehicles. Travel speeds may vary over a 24hr period.

    • Determine the average travel speeds during your simulation period and adjust the Speed Distribution accordingly

  • A Vissim project’s first highway off-ramp is often the cause of unrealistic congestion due to simulated vehicles waiting to merge

    • Extend the first/entry ML link right before the nearest upstream ramp

    • This assures more vehicles will generate from the ML Vehicles Input and not be blocked due to congestion.

  • Double Click the off-ramp’s connector (not the link) to open the connector menu (see Figure below)

    • Under the “Route” section, increase the “Lane Change” value to the distance between the off-ramp and the ML entry

    • Another method would be to Check the box “per lane” and increase the “Lane Change” value

 
 

  • After adjusting a few Driving Behavior Parameters, run the simulation again and calculate the GEH with your new Simulation volumes

  • Repeat this section until your project meets the required acceptance criteria

TIP: Many simulations will be required to complete this project. Since each simulation requires a significant amount to time to complete, consider calculating every GEH value while the simulation runs. As one team member runs and monitors the simulation, another team member will calculate the GEH values. Only adjust Driving Behavior Parameters one at a time and by 10% to 25%.