Editing the driving behavior parameter Following behavior

Look ahead distance

Minimum, Maximum: Minimum and maximum distance to preceding vehicles that a vehicle can see in order to react to other vehicles and interaction objects downstream along its route or path. The vehicle takes into account the look ahead distance in addition to the entered number of interaction objects.

The look ahead distance has an effect on

• the vehicle’s movement when approaching a stationary obstacle. The vehicle will then slow down evenly.
• the perception of link intermediate points with the Brake radius effect, if the option speed limitation in curves is selected in the network settings for driving behavior (Selecting network settings for vehicle behavior).

The Minimum look-ahead distance is important when modeling the lateral behavior of vehicles.

• If the minimum look ahead distance is 0.00, only the number of interaction objects applies which is specified in the attribute Number of interaction objects.
• If several vehicles can overtake within a lane, this value needs to be greater than 0.00, e.g. in urban areas, depending on the speed, the look ahead distance might be approx. 20-30m, with correspondingly larger values for outside of the city. This way you avoid that during the simulation the impression is created that one vehicle is passing through another vehicle. This may happen when there are more vehicles than specified in the Number of interaction objects attribute that want to position themselves in front of a stop line on the same link. This applies in particular to bicycles.
• If several vehicles can overtake within a lane, you can enter a greater look ahead distance to prevent any vehicles from running a red light. When doing so, do not change the number of Observed vehicles. This can lead to an unrealistic simulation.

Only the Maximum look-ahead distance needs to be extended, e.g. to model rail traffic with block signals (Modeling railroad block signals).

Number of interaction objects

Number of preceding vehicles and/or number of network objects listed below which the vehicle perceives along its route or path in order to react to them. In addition to the number of observed vehicles entered, vehicles take the minimum and maximum Look ahead distance into account.

In Vissim, the following network objects are modeled as vehicles. Vehicles treat these network objects as a preceding vehicle. These network objects act like a red signal head. If there are several of these network objects within a very short distance, enter a larger number for the Number of interaction objects. However, this can lead to slightly longer simulation computation times.

• Red signal heads
• Reduced Speed Areas
• Priority rules for cases in which the minimum time gap or minimum clearance is not kept.

Vehicles also treat the following network objects as a preceding vehicle, when they have to stop there:

• Stop Signs
• Public transport stops
• Parking Lots

Behavior in conflict areas: A vehicle takes into consideration all downstream conflict areas, up to the furthest interaction object specified under the number of interaction objects. To include conflict areas in the Number of interaction objects, for the applicable driving behavior, select the attribute option Conflict areas count as interaction objects (Editing the driving behavior parameter driver error).

Default values of Number of interaction objects for predefined driving behavior:

• Urban (motorized): 4
• AV aggressive (CoEXist): 10
• All other predefined driving behaviors: 2

In the Number of interaction vehicles attribute, you can limit the number of vehicles considered independently of other network objects. The vehicle is maximally aware of the Number of interaction objects.

Link intermediate points with the Brake radius effect are recognized by the vehicle within its look ahead range, but they are not counted as interaction objects.

Number of interaction vehicles

Number of preceding vehicles that the vehicle perceives along its route or path in order to react to them.

The vehicle looks at the maximum number of interaction objects (vehicles and network objects) along its route or path, if the minimum look ahead distance does not force it to look further. The vehicle only considers the maximum number of vehicles specified in the Number of interaction vehicles, it still considers other network objects. Thus, a number of interaction vehicles >= number of interaction objects has no effect.

Example: Set the value Number of interaction vehicles =1 to model an autonomous vehicle whose sensors should not be able to detect other vehicles through a vehicle in front, but should be able to detect all traffic signs with the help of Car2X communication.

Look back distance

Minimum, Maximum: The look back distance defines the minimum and maximum distance to vehicles that a vehicle can see behind it in order to react to other upstream vehicles. The look back distance only affects the vehicle’s perception of other vehicles, it does not perceive other interaction objects.

The number of interaction objects within the Look back distance is only taken into account when calculating the vehicle’s lateral behavior. In all other cases, the vehicle perceives a maximum of one other vehicle when looking back.

Lateral behavior: Effect of the minimum look back distance:

If several vehicles can overtake within a lane, this value needs to be greater than 0.00, e.g. in urban areas it could be 20-30m, with correspondingly larger values in other places. This way you make sure the cars drive in an orderly fashion, when on the same route two or more vehicles than specified in the attribute Number of interaction objects want to position themselves at a stop line. This applies in particular to bicycles.

You can reduce the maximum look-back distance in close-meshed networks, e.g. with many connectors over a short distance. This may positively affect the simulation speed.

Standstill distance for static obstacles

Standstill distance (ax) for vehicles upstream of static obstacles. These are, for example, signal heads, stop signs, bus stops, priority rules, conflict areas. Not valid for stop signs in parking lots.

Minimum value: 0.01 m, maximum value: 10 m, default value: 0.5 m. If you open an *.inpx file where the attribute value is 0, the value is changed to 0.01 m.

You can also use this standstill distance to define the stopping position of public transport vehicles at stops with platform screen doors and queues at fixed positions on the platform. The public transport vehicle stops at the stop with its front edge at the standstill distance (ax)+ 1 m position. The one meter ensures that the public transport vehicle can exit from the stop. To allow boarding and alighting, the length of the stop must be at least equal to the length of the public transport vehicle + standstill distance (ax)+ 1 m.

Vehicles stop in front of signal heads at standstill distance (ax)+ 0.5 m.

Jerk limitation (JerkLimit)

•  If the option is enabled, the adjustment of vehicle acceleration is restricted between two consecutive time steps.
•  If the option is not chosen, acceleration of the vehicle can vary arbitrarily between two time steps. For example, a vehicle accelerating from a standstill can achieve its desired acceleration.

In the following situations, no jerk limitation occurs, even if the Jerk limitation option is selected:

• The vehicle is changing lanes.
• The vehicle reaches a speed ≤10^-6m/s within 1 s.
• The vehicle performs emergency braking (interaction state Brake AX).
• The Pedestrian category is selected for the vehicle type.
• The absolute value of the desired change in acceleration is ≤ 0.2 m/s2. With a time step of 0.05 s, no jerk limitation occurs if the change is ≤ v0.1 m/s2.
• The time step is ≥0.5 s.
• The vehicle is controlled via an external driver model DLL file.
• The vehicle is a trailing vehicle in a platoon.
• The vehicle is controlled via the driving simulator interface.