Decision models for lane changes

In Vissim, vehicles can perform different types of lane changes, which are each based on individual decision models:

• Mandatory lane change (Mandatory lane change)
• Free lane change (Free lane change)
• Automatic lane change (Automatic lane changes)

Mandatory lane change

The vehicle performs a lane change required to reach the next connector of a vehicle route. These are triggered by:

• the vehicle route
• in the context of dynamic assignment by the path
• when a desired lane is set via the COM interface

For a mandatory lane change, the driving behavior parameters contain the maximum acceptable deceleration for the lane changing vehicle and its trailing vehicle on the new lane. The deceleration depends on the distance to the emergency stop distance of the next route connector.

Free lane change

The vehicle performs a free lane change, if more space is available on the new lane or if longer driving at the desired speed is required:

When a free lane change is performed, Vissim checks whether both desired safety distances are maintained on the new lane:

• the desired safety distance of the trailing vehicle to the lane changing vehicle
• the desired safety distance of the lane changing vehicle to its preceding vehicle

The safety distance reduction factor is applied to both desired safety distances.

By default, a lane change takes 3 seconds.

You cannot change the degree of "aggressiveness" for free lane changes. You can, however, influence free lane change by changing the safety distance. You set the safety distance values in the model parameters of the car following model (Editing the driving behavior parameter car following model).

In both cases of lane change, upstream and downstream, the Min. clearance must be respected (Editing the driving behavior parameter Lane change behavior).

When deciding on a lane change to overtake a slow vehicle, a vehicle considers its own current maximum speed depending on the lane change behavior:

• when the lane change behavior Free lane selection is selected
• when the lane change behavior Slow lane rule, Fast lane rule is selected and the preceding vehicle or the neighboring vehicle is driving slower than 60 km/h and therefore the rule is ignored

Since the maximum speed is defined by the maximum acceleration and the current gradient, taking the maximum speed into account prevents HGVs from starting to overtake on gradients, for example, without being able to overtake because they cannot reach their desired speed.

In 2D animation, a current change of lanes, as well as the desire to change lanes is visualized via a small red line to the right or left of the vehicle (representing the turn signal), from the defined Lane change distance on. In 3D animation, a current lane change and the desire to change lanes is shown via a turn signal, if this is defined for the 3D model of the vehicle.

Automatic lane changes

Autonomous vehicles (ego vehicles) perform automatic lane changes voluntarily and independently. Automatic lane changes are based on the Automatic Lane Change (ALC) decision model (How the Automatic Lane Change (ALC) Decision Model works). This decision model does not apply to mandatory lane changes (Mandatory lane change).

For the automatic lane change, the applicable General behavior, either the Slow lane rule or Left side rule must be selected. This rule is typically mandated on highways or expressways with several lanes. Since autonomous vehicles are equipped with distance control, the car following model Adaptive Cruise Control (ACC) must be selected (Editing the driving behavior parameter car following model), (Operation of the Adaptive Cruise Control (ACC) vehicle following model).