Attributes for path selection

1. On the Traffic menu, click > Dynamic Assignment > Parameters.

The Dynamic Assignment: Parameters window opens.

2. Select the Choice tab.

3. Make the desired changes:

Element	Description
Destination parking lot selection
Logit scaling factor	Sensitivity parameter of the Logit function for the parking lot selection model
Logit lower limit	Lowest selection probability which is still taken into account when choosing a parking lot. Parking lots with lower selection probability are not selected.
Path pre-selection
Reject paths with too high total cost	When this option is selected, the Max. extra cost compared to the best path: box is selected. Vehicles avoid paths identified as too expensive Paths are too expensive if the generalized costs exceed the costs of the best path of the corresponding parking lot relation by the specified factor (in %).
Max. extra cost compared to the best path	Threshold in % for the cost difference as a criterion for path selection.
Limit number of paths	If this option is selected, the option below it Max. number of paths per parking lot relation: is activated. Vehicles consider the specified number of paths at most for a parking lot relation. This attribute is only effective during dynamic assignment and not when you read paths (Setting volume for paths manually).
Max. number of paths per parking lot relation	Maximum number of paths per parking lot relation as a criterion for path selection. Default 999.
Avoid long detours	If the option has been selected, vehicles avoid paths that they identify as detours. A path is a detour if it replaces a section of an existing path with a section which is longer by at least the specified factor (Using the detour factor to avoid detours). The option Stochastic assignment (Kirchhoff) or Equilibrium assignment must be selected.

4. In the Path choice model section, select the desired procedure:

Element	Description
Use volume (old)	The path is selected without a path search for new paths being carried out. The probability of a path being used corresponds to its attribute value Volume (old) share in the total of attribute values Volume (old), of all paths of the same parking lot relation. This volume data for all intervals is read in from the Path file at the beginning of each simulation run. It is then moved to the Paths list, to the Volume (old) attribute. With the Volume (new) attribute for paths, the vehicles are counted that use the respective path during the simulation run (Attributes of paths). You can set the volume to the paths of a time interval that has not yet started during the simulation interval or to a time interval prior to the simulation run (Setting volume for paths manually). If ANM routes are imported as paths for dynamic assignment, the ANM import function automatically selects the attribute Use volume (old).
Stochastic assignment (Kirchhoff)	The path is selected based on path search for new paths and an evaluation of the costs according to Kirchhoff. In the Costs tab, select the calculation procedure used as a basis to calculate the costs for path selection according to Kirchhoff. Kirchhoff exponent: Sensitivity parameter of the distribution function for path selection model. Default 3.50. Correction of overlapping paths: If this option is selected, it activates the correction of the distribution of traffic on paths which have legs in common (Correcting distorted demand distribution for overlapping paths). The attribute Kirchhoff (edge travel times) must be selected.
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 amount of the transferred 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. Current Iteration: Number of simulation runs performed ► On the Cost tab, in the section Time interval for edge travel times in path search, select Same time interval, previous simulation run (Attributes for calculating costs as a basis for path selection). If you select Equilibrium assignment, the smoothing method is not relevant (Attributes for calculating costs as a basis for path selection). Vissim then uses the smoothing factor 1.0. This means no smoothing.is performed. ► On the Search tab, below Path selection type, select Decide at start only. Ensure that the option Decide repeatedly is deselected (Attributes for path search).

Element

Description

Use volume (old)

The path is selected without a path search for new paths being carried out.

The probability of a path being used corresponds to its attribute value Volume (old) share in the total of attribute values Volume (old), of all paths of the same parking lot relation. This volume data for all intervals is read in from the Path file at the beginning of each simulation run. It is then moved to the Paths list, to the Volume (old) attribute. With the Volume (new) attribute for paths, the vehicles are counted that use the respective path during the simulation run (Attributes of paths).

You can set the volume to the paths of a time interval that has not yet started during the simulation interval or to a time interval prior to the simulation run (Setting volume for paths manually).

If ANM routes are imported as paths for dynamic assignment, the ANM import function automatically selects the attribute Use volume (old).

Stochastic assignment (Kirchhoff)

The path is selected based on path search for new paths and an evaluation of the costs according to Kirchhoff. In the Costs tab, select the calculation procedure used as a basis to calculate the costs for path selection according to Kirchhoff.

Kirchhoff exponent: Sensitivity parameter of the distribution function for path selection model. Default 3.50.
Correction of overlapping paths: If this option is selected, it activates the correction of the distribution of traffic on paths which have legs in common (Correcting distorted demand distribution for overlapping paths). The attribute Kirchhoff (edge travel times) must be selected.

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 amount of the transferred 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.

Current Iteration: Number of simulation runs performed
► On the Cost tab, in the section Time interval for edge travel times in path search, select Same time interval, previous simulation run (Attributes for calculating costs as a basis for path selection).

If you select Equilibrium assignment, the smoothing method is not relevant (Attributes for calculating costs as a basis for path selection). Vissim then uses the smoothing factor 1.0. This means no smoothing.is performed.

► On the Search tab, below Path selection type, select Decide at start only. Ensure that the option Decide repeatedly is deselected (Attributes for path search).

5. Confirm with OK.

Superordinate topic:

Controlling dynamic assignment

Information on editing:

Controlling iterations of the simulation

Setting volume for paths manually

Influencing path search

Evaluating costs and assigned traffic of paths