Using lateral drift speed

You can define monotonically increasing functions for lateral drift speed. They allow you to determine the lateral drift speed of the vehicle for the speed ratio, which is calculated using the Critical speed function.

Vissim uses the Lateral drift speed function to calculate the lateral offset Lateral deviation (excessive speed) for vehicles that change their lateral position due to excessive speed. A vehicle whose Radius attribute corresponds to the Radius of curvature value x is carried out of a curve at a 3D point or drifts sideways.

In the Vehicles in the network list, you can display the Lateral deviation (excessive speed) of the vehicle (Displaying vehicles in the network in a list).

1.  On the Base Data menu, click > Functions > Lateral drift speed.

The list of defined objects for the base data type opens.

By default, you can edit the list (Using lists).

2.  In the list on left, on the toolbar, click the Add button .

3.  In the Name table field, enter a name for the function.

4.  Repeat the following steps for the desired number of data points. Repeat the following steps for the desired number of data points.

The window of the function opens.

5.  Click the start point or end point of the curve whose value you want to change, hold down the mouse button and drag the point to the desired value.

6.  Right-click in the line.

7.  From the shortcut menu, choose Add new point.

A node is entered.

8.  Click the intermediate point and keep the mouse button pressed.

9.  With the mouse button pressed, drag the intermediate point to the desired position.

10.  Release the mouse button.

11.  Confirm with OK.

The function is displayed in the list Lateral Drift Speed Function on the left. In the Data points list, on the right, the minimum value, maximum value and the inserted intermediate points are displayed.

Element	Description
x	Speed ratio: Current vehicle speed / critical speed in Critical speed function of the vehicle type (Defining curve speed). Threshold value from which lateral drift speed y is used to calculate the lateral offset. Default value 1.0.
y	Lateral drift speed: Speed [m/s] used for speed quotient x at which the vehicle changes its lateral position. The function value is linearly interpolated between several interpolation points.

12.  Assign the function as an attribute to those vehicle types you wish to impact (Attributes of vehicle types).

13.  Make sure that the value Drift is selected for all relevant link intermediate points for the Radius effect attribute.