Modeling vehicle inputs for private transportation

In the network, you can define time-dependent vehicle inputs for all vehicle types. You can allocate one or several vehicle compositions to a vehicle input (Attributes of vehicle inputs), (Modeling vehicle compositions). If for a link, you allocate a vehicle composition with one vehicle type each to several vehicle inputs and select Volume type > Exact, you can define the exact number of vehicles of each vehicle type entering this link. During the simulation period, Vissim generates individual vehicles for vehicle inputs at a random point of time based on vehicle compositions and the volumes entered.

Vehicle inputs may be positioned on links only. A vehicle input cannot be placed on a single lane of a link.

Time intervals for vehicle inputs

You can create time intervals for vehicle inputs and thus determine the volume for each time interval in a vehicle input. You enter the volume for a link in vehicles per hour. With the Volume type, you can choose to use the exact number of vehicles or have Vissim select a number stochastically based on the input volume (Attributes of vehicle inputs). You must always enter the number of vehicles per hour, even if the time interval is shorter or does not end at a full hour, e.g. after 3.5 hours.

Vehicle entry times

The time when the vehicles enter a link in the Vissim network is defined by Vissim stochastically: An average time gap between two vehicles results from the hourly volume. This average gap is used as an average value of a negative exponential distribution from which Vissim draws the gaps. This is equivalent to a Poisson distribution of the input times. In real life scenarios, the entry time may be subject to greater variability than in Vissim on the basis of the Poisson distribution.

If the vehicle input specified for the network during a simulation time interval is exceed by more than two vehicles, a corresponding message is displayed.

• The message and time interval per vehicle input are saved to the * .err file.
• When you exit the simulation run, a window opens displaying the message. In this window, you can open the Messages window. It shows this and other messages, if there are any.
• The *.err file does not contain any messages if vehicles are not input because the vehicle input interval is longer than the simulation time. The maximum possible traffic volume depends on the speed and the driving behavior parameters which have been set.

Lane selection when entering a vehicle into the Vissim network

The vehicle must be assigned to a vehicle type that is allowed in the lane of the link on which the vehicle input is placed (Attributes of links).

If a link has multiple lanes in which the vehicle can be entered, Vissim will introduce the vehicle in the lane that provides the longest collision time for the vehicle. That is the lane in which the vehicle can drive the longest without reaching a preceding vehicle or network object that has an impact on its desired speed, e.g. a signal controller, a priority rule or a conflict area.

If a link has two lanes, one of which is a passing lane and the other one is closed to all vehicle classes, Vissim will operate the vehicle on the closed lane.

Vehicle speed used in network

When calculating the speed of a vehicle within the Vissim network, e.g. in an input flow or during dynamic assignment, on a parking lot of a zone connector, Vissim accounts for the distance between the vehicle and its preceding vehicle as well as for the maximum look ahead distance. The look ahead distance on the respective link applies to the driving behavior of the vehicle type that the vehicle is assigned to.

• If the distance is greater than the maximum look ahead distance, the vehicle moves at its desired speed.
• If the distance is less than the maximum look ahead distance, but greater than the safety distance, the following applies: v = DesSpeed - (DesSpeed - vPrecedingVehicle) * (1 - dx / maximum look ahead distance).
• If the distance is less than the safety distance, the vehicle is not used.

Demand in origin-destination matrices for dynamic assignment

For dynamic assignment, you do not need to define any vehicle inputs, as the demand is contained in the origin-destination matrices (Using dynamic assignment).