Editing the driving behavior parameter Following behavior

Look ahead distance

Minimum, Maximum: Minimum and maximum distance that a vehicle can see forward in order to react to other vehicles and interaction objects that are in front of or next to it on the same link. Vehicles take into account the minimum and maximum look-ahead distance in addition to the entered number of interaction objects. Even when driving up to a stationary obstacle, vehicles reduce their speed evenly on the basis of the look ahead distance.

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 downstream or adjacent to it on the same link 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.

Default number of interaction objects for predefined driving behavior:

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

In the attribute Number of interaction vehicles, under Number of interaction objects, you can specify the number of vehicles that Vissim takes into account in addition to the above-mentioned network objects. The vehicle is maximally aware of the Number of interaction objects.

Number of interaction vehicles

Number of preceding vehicles which the vehicle perceives downstream or adjacent to it on the same link in order to react to them.

• The Number of Interaction vehicles is included in the Number of interaction objects.
• The Number of interaction vehicles does not include the network objects listed in the description of the attribute Number of interaction objects and those that the vehicle perceives as a vehicle.
• The vehicle is maximally aware of the Number of interaction objects.

Default value for all predefined driving behaviors: 99 vehicles.

For example, if you are modeling an autonomous vehicle whose sensors are blocked through a preceding vehicle which is preventing it from detecting other vehicles, set the Number of interaction vehicles to 1.

Look back distance

Minimum, Maximum: The Look back distance defines the minimum and maximum distance that a vehicle can see backwards in order to react to other vehicles behind it (on the same link).

The minimum look-back distance is important when modeling lateral vehicle behavior.

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.

Temporary lack of attention

• Duration: The period of time when vehicles may not react to a preceding vehicle. They do react however to emergency braking.
• Probability: Frequency of the lack of attention

With increasing values, the capacity of the affected links decreases.

Standstill distance for static obstacles

Standstill distance (ax) 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. The attribute Smooth closeup behavior must be selected.

 If this option is not selected, the vehicles use a normally distributed random value [0.5; 0.15].

 If the option is selected, vehicles use the entered value. Activate this option for PT vehicles at PT stops with platform screen doors and queues at fixed positions on the platform.

Maintain absolute braking distance

EnforcAbsBrakDist: For braking, the vehicle accounts for the distance necessary to stop without causing a collision should the vehicle in front it stop immediately without a braking distance. The absolute braking distance applies to vehicles in the following cases:

• Following behavior: The desired safety distance corresponds to at least the absolute braking distance.
• Lane change: When deciding to change the lane, the vehicle takes into account the absolute braking distance to both the new vehicle preceding it and to the new vehicle following it. If the absolute braking distance is not sufficient, the vehicle does not change the lane.
• For following behavior and lane changes the following applies: If for the vehicle the car following model Wiedemann 74 is selected, the standstill distance ax is added to calculate the absolute braking distance for other vehicles. If the car following model Wiedemann 99 is selected, instead the standstill distance CC0 is added.
• In a crossing conflict, the vehicle travels the conflict area in the subordinate flow, if the vehicle in the main flow can maintain the absolute braking distance.
• Vehicle inputs: The vehicle is inserted into the Vissim network with at least the absolute braking distance.
• Conflict areas:The absolute braking distance applies to vehicles that are involved in the conflict and have priority: The vehicle is inserted into the Vissim network with at least the absolute braking distance. The gap time the vehicle with the right of way needs to come to a stop before the conflict, is calculated by Vissim from the current speed of the vehicle and the maximum deceleration possible at this speed. The time it takes the other vehicle to cover a distance of 1 m, driving at its current speed, is added to the gap time.

The absolute braking distance is not effective where priority rules are used.

Use implicit stochastics

UseImplicStoch:

 If this option is selected, Vissim uses a variable stochastic value for the following attributes and for the estimation uncertainty, which takes into account variations in human perception. This variable stochastic value is based on a) the time distribution CC1 (for the speed-dependent part of the desired safety distance) and b) on internal distributions that apply to the desired acceleration and deceleration:

• Safety distance
• Desired Acceleration
• Desired Deceleration
• Minimum lateral distance

 If the option is deselected, Vissim uses non-variable deterministic values that are based on the meridian of the time distribution CC1 (for the speed-dependent part of the desired safety distance) and of internal distributions that apply to the desired acceleration and deceleration.