Transportation Systems Simulation - A Tutorial for Multi-Modal Simulation Using VISSIM/Freeway: Improving Results

After the first simulation, you may have encountered unusual behavior. VISSIM v7 has tools to adjust a few driving parameters.

Adjusting Driving BehaviorEdit

Every link and connector can have a unique Behavior Type. Under “Network Objects” Right Click “Links” and Select “Show List” (see Figure below). 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
Wiedemann 99 is suitable freeway traffic with no merging
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)Edit

  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 (Figure 44)

  • 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 Figure 46. 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)Edit

  • “Lane Change” tab and General behavior: “Free lane selection” or “Slow lane rule”
  • Check the “Cooperative lane change” box (see Figure below)

WARNING: It is not recommended to adjust Lane Change parameters until all previous steps have been attempted.

After adjusting a few Driving Behavior Parameters, run the simulation again and calculate the GEH with your new Simulation volumes. Only adjust Driving Behavior Parameters one at a time and by 10% to 25%.

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