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 Behavior
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)

 * 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)

 * “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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