Path choice models for distributing demand data to the paths

The distribution of demand data to the paths can be done according to the following path choice models (Attributes for path selection):

• Use volume (old): Base path search exclusively on volumes of previous simulation runs. These may stem from a previous simulation run or an ANM import.
Stochastic assignment (Kirchhoff): The distribution is carried out in each iteration according to Kirchhoff based on the smoothed generalized costs of the previous iteration. Less vehicles use paths with higher costs than paths with lower costs. Paths with the same cost get the same volume, regardless of their capacity. The result of the assignment is the following distribution to the paths:
• Paths with higher volumes have lower costs
• Paths with lower volumes have higher costs
• Paths with identical volumes have identical costs
Equilibrium assignment: Redistributes demand across paths proportionally to costs, from expensive to inexpensive paths, for each OD pair in each iteration: The volume of paths that are more expensive than the average is reduced. The height of the specified volume is proportional to the additional costs of the path. All paths that are cheaper than the average path costs are assigned additional volume. The additional volume is proportional to the cost saving compared with the average path costs (Method of path selection with or without path search). The result of the assignment are identical generalized costs on all paths of a parking lot OD pair, possibly with very different volumes, dependent on the respective capacity of the path.

Choose whether you want path selection to be based on the travel time measured on paths or on the total of travel times on edges. In doing so, you define the calculation of generalized costs. The desired method of cost calculation can be selected in the parameters of dynamic assignment Cost for path distribution with Kirchhoff: (Attributes for calculating costs as a basis for path selection).

Path pre-selection takes precedence over path choice model when selecting paths

Vissim executes the path selection in two steps:

Make a path pre-selection

Path pre-selection is based on the criteria selected for the Path pre-selection attribute (Attributes for path selection). Vissim only takes into account paths that are not blocked for a vehicle class due to one of the following criteria:

• The path contains a complete route closure.
• The path is closed for a vehicle class if the path contains part of a connector that is closed for dynamic assignment for this vehicle class.

When reading the path file, Vissim already excludes paths that contain a closed edge. This means that these paths are not included in the path pre-selection.

Apply path choice model

After pre-selection, Vissim chooses the path that a vehicle in the given vehicle class will follow based on the selected distribution model.

Notes: If you want to reproduce the results of an assignment using the path choice model Use volume (old) (Attributes for path selection), make sure that: Either the Path pre-selection is disabled (Attributes for path selection) or make sure that it does not change. For each OD relation with a demand > ZERO, there must be at least one path with a volume > ZERO. If all path volumes are ZERO for an OD relation with demand, vehicles will still travel on this OD relation. These vehicles will select a path from the set of paths for the OD relation in an evenly distributed manner.