The Nested demand calculation is a variant of the standard 4-step model to calculate demand. The calculation is based on a Nested Logit model which presupposes the specification of choice model structures for each demand stratum. A choice model structure may be a nested mode choice but also a nested model with destination choice, mode choice, and choice of the time-of-day alternative in general (Fundamentals: Nested demand model).
1. On the toolbar, click the 
Open 'Procedure sequence' window button.
The Procedure sequence window opens.
2. To the procedure sequence, at the position of your choice, add the procedure Nested demand of the Demand model category (Setting up and starting the procedure sequence).
3. In the row of the added procedure, click on the button in the Reference object(s) column.
The Demand strata selection window opens.
4. In the Select demand model list, click the demand model the demand strata belong to.
5. In the Demand stratum selection list, select the demand strata you would like to calculate the nested demand for.
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Tip: To select multiple demand strata, hold down the Ctrl while clicking the desired entries one by one. |
6. Confirm with OK.
The demand strata selected are listed in the Reference object(s) column.
7. Make sure the added procedure is highlighted. Then, in the Operations section, click the Edit button.
The Parameters: Nested demand window opens.
8. Make the desired general settings for all demand strata.
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Element |
Description |
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For active OD pairs only |
If this option has been selected, only those OD pairs which are in the active state are considered (Exception: Filter for OD pairs). |
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Exclude OD pairs connecting passive zones |
If this option has been selected, only OD pairs between active zones are considered (Using filters to set network objects active or passive and Selecting network object types for the spatial selection mode). |
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Set any result demand matrix to 0 prior to calculation |
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Save old result demand matrices for gap calculation |
If this option has been selected, already existing result demand matrices will be saved prior to the calculation. They are required for the procedure Nested demand gap calculation. |
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Model form |
There are two variants to calculate the demand (Fundamentals: Absolute and incremental calculation):
In the absolute calculation, the demand is calculated from scratch. The prerequisite is that attraction and production have been calculated with the Trip generation procedure (Calculating trip generation).
In case of an incremental calculation, cost changes and a basic demand are prerequisite for a calculation of the resulting modified demand. |
If this option has been selected, the result demand matrices are set to zero.
If the option has not been selected, the result demand matrices remain unchanged.9. Make the desired changes on the Choice model structures tab.
If required, you can create a choice model structure for each demand stratum and a maximum of one choice level per choice type for each choice model structure (You can create a maximum of one choice level per choice type for each choice model structure. Use the icons to create or delete a new choice level.).
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Choice model structures tab |
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Element |
Description |
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Choice type |
Choice type of the choice level |
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Alternatives |
Alternatives valid for the choice level |
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Save demand |
If the option is selected, the original demand for the choice type of the level is saved for all demand strata, which use this model structure. |
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Save logsums |
If the option is selected, the logsums calculated on this level are saved for all demand strata, which use this model structure. In case of a nested mode choice, the logsums of the root node are output. |
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Opens the Create choice model structure window in which you can enter a code for the choice model structure. |
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Copies the marked choice model structure. |
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Opens the Edit choice model structure window in which you can edit the code of the choice model structure. |
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Deletes the marked choice model structure. |
You can create a maximum of one choice level per choice type for each choice model structure. Use the icons to create or delete a new choice level.
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Section Choice levels |
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Element |
Description |
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The Create choice level window opens. Each type of the choice level can be inserted only once into a choice level. |
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Deletes the marked choice levels from the choice model structure. |
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Moves the marked choice levels one row up in the list. |
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Moves the marked choice levels one row down in the list. |
1. Click the 
Create choice level icon.
2. In the drop-down list, select the desired choice type.
3. Confirm with OK.
4. In the row of the desired choice level Time-of-day choice or Mode choice, click in the 
icon in column Alternatives.
5. Make the desired changes:
- Edit time-of-day alternatives
Time-of-day alternatives must be sorted in ascending order of time.
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Icon |
Name |
Description |
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Create time-of-day alternative |
Adds a new time-of-day alternative TimeOfDay with an ascending number to the list. You can edit the Code. As a rule, the time-of-day alternatives AM (morning peak, IP (inter-peak) and PM (afternoon peak) are used. The table is sorted from the earliest time-of-day alternative (top) to the latest time-of-day alternative (bottom). |
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Delete marked time-of-day alternatives |
Deletes the marked time-of-day alternatives from the list. |
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Move marked time-of-day alternatives upwards |
Moves the marked time-of-day alternatives one row up in the list. |
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Move marked time-of-day alternatives downwards |
Moves the marked time-of-day alternatives one row down in the list. |
- Edit decision tree
How to edit the decision tree for the mode choice is described with procedure Tour-based model - Combined trip distribution / mode choice ( >> Nested Logit model: Edit decision tree1. Make sure of the following:in the procedure sequence, the Tour-based model - Combined trip distribution / mode choice procedure has been created (Calculating tour-based model - combined trip distribution and mode choice)The Parameters: Tour-based model - Combined trip distribution / mode choice window is open.2. Select the Mode choice utility tab.3. Choose the option Use nested logit model for mode choice.4. Click the Decision tree button.A query might open. Click Yes to confirm the query, to apply the utility definition and the scaling factor of person groups / destination activity / mode with Logit function type in the Nested Logit model. The Edit decision tree window opens and the existing root nodes for the decision tree are displayed.5. Make the desired settings.ElementDescription Create nested nodeThe Create nested node window opens, in which you can create nest nodes underneath the root node (Create nested node). Create mode nodeThe Create mode node window opens, in which you can allocate a new mode node to a nest node (Create mode node). Edit marked nest/mode node.Opens the Edit nest/mode node window (Edit nest or mode node) Delete marked nest/mode node.Deletes a marked nest or mode node.NoteYou cannot delete the root node. For each mode, there must be at least one mode node in the decision tree, so that you cannot delete the last mode node of an existing mode.Create nested nodeYou can create additional nested nodes underneath each nested node. The number of levels is not restricted by Visum. If, however, you would like to use the Cross Nested Logit model for which a mode is allocated to a number of nest nodes, you should not nest the nest nodes (Fundamentals: Calculating tour-based model - combined trip distribution and mode choice).1. Make sure that the Edit decision tree window is open.2. Click the Create nested node icon.3. Make the desired changes ElementDescriptionParent nodeSelection of the parent node under which the new nest node is createdName of the nodeUnique name of the nest node4. Confirm with OK.Create mode node1. Make sure that the Edit decision tree window is open.2. Click the Insert mode node icon.3. Make the desired changes ElementDescriptionParent nodeSelection of the parent node under which the new nest node is createdMode nameSelection of the mode for the mode nodeEdit nest or mode node1. Make sure that the Edit decision tree window is open.2. Click the Edit marked nest/mode node icon.3. Make the desired changes.ElementDescriptionEdit nested nodeParent node selection listSelection of the parent node under which the nest node is createdName of the nestRenaming the network nodeEdit mode nodeParent node selection listSelection of the parent node under which the mode node is created © 2022 PTV Planung Transport Verkehr GmbH). Follow the instructions from step 5.
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Note: Cross Nested Logit is not possible during the Nested demand procedure. |
6. Make the desired changes in the Distribution tab.
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Distribution tab |
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Element |
Description |
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Demand stratum |
Demand strata set in column Reference object(s) for procedure Nested Demand |
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Choice model structure code |
Selection of the choice model structure code for the demand stratum |
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Trip form |
Selection of the kind of demand:
Note If the OD (one trip) option has been selected, time-of-day alternatives correspond to time periods. If the PA (two trips) option has been selected, time-of-day alternatives correspond to a combination of two time periods: one in which the outward journey takes place and one in which the return journey takes place. The return journey must take place in the same time-of-day period or afterwards. Possible alternatives are determined by the chronological order. They correspond to combinations of two time periods (Fundamentals: Trip form in combination with time of day choice). |
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First column Input demand matrix |
Click the Note The matrix is only required if no choice type Destination choice is calculated. |
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Second column Input demand matrix |
Display of the input demand matrix |
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Attraction attribute |
Selection of a zone attribute for the attraction If no selection has been made, attribute Attraction (<Demand stratum>) will be used. Note The attribute is only available if the choice type Destination choice is calculated. |
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Normalization mode |
Scaling of the attractions Note The attribute is only available if the choice type Destination choice is calculated and absolute is selected as the model form. |
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Constraint type |
Selection of the constraint type:
Note The attribute is only available if the choice type Destination choice is calculated (Fundamentals: Singly or doubly-constrained destination choice). |
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Group for doubly-constrained distribution |
Displays the demand strata that are balanced together. If the value is empty, the demand stratum forms its own group. |
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Maximum number of iterations |
Maximum number of iterations before the procedure is terminated. Note The option is only available if the doubly-constrained option has been selected in the Constraint type column. |
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Tolerance |
Termination criterion. The calculation is terminated if the tolerance value or the maximum number of iterations is reached. Note The option is only available if the doubly-constrained option has been selected in the Constraint type column. |
7. Make the desired changes on the Utility tab.
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Utility tab |
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Element |
Description |
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Key |
Unique value generated by Visum for each combination of Demand stratum and Mode and Time-of-day, where applicable |
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Demand stratum |
Code of the demand stratum |
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Mode |
Code of the mode if a mode choice is calculated |
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Time-of-day |
Code of the time-of-day if a time-of-day choice is calculated |
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Utility function |
Click the |
8. Make the desired changes in the Output / basic demand tab.
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Note: The sections of the tab on basic demand are only displayed in case of an incremental calculation (Fundamentals: Calculation for the incremental model form). |
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Output / basic demand tab |
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Element |
Description |
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Key |
Unique value generated by Visum for each combination of Demand stratum and Mode and Time-of-day, where applicable |
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Demand stratum |
Code of the demand stratum |
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Mode |
Code of the mode if a mode choice is calculated |
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Time-of-day |
Code of the time-of-day if a time-of-day choice is calculated |
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First column Result demand matrix |
Click the button to open the Select matrix window, in which you can select a demand matrix for zones as result demand matrix (Selecting matrices). |
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Second column Result demand matrix |
Display of the result demand matrix |
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First column Base demand matrix |
Click the button to open the Select matrix window, in which you can select a demand matrix for zones as base demand matrix (Selecting matrices). |
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Second column Base demand matrix |
Display of the matrix selected in the first column |
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First column Last demand matrix |
Use the button to open the Select matrix window, in which you can select a result demand matrix for zones as result demand matrix (Selecting matrices). Note The column is only displayed if option Save old result demand matrices for gap calculation has been selected. |
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Second column Last demand matrix |
Display of the last demand matrix |
9. Specify the settings you need on the Alternative-specific constants tab.
The Alternative-specific constants tab is only displayed if you have selected the option absolute under Model form and an absolute calculation is to be carried out. For each choice model structure, a new tab is displayed. On those tabs, you can specify the respective alternative-specific constants (Fundamentals: Alternative-specific constants (ASC)). The definition of the constants is optional.
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Alternative-specific constants tab |
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Element |
Description |
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Key |
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<Code of the demand stratum> columns |
Use the |
10. Make the desired changes on the Scaling parameters (lambda) tab.
For each choice model structure, a new tab is displayed. On those tabs, you can specify the respective scaling parameters (lambda) (Fundamentals: Scaling parameters (λ)). The definition of the constants is optional.
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Scaling parameters (lambda) tab |
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Element |
Description |
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Key |
Displays the alternative of the choice type |
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Choice type |
Displays the choice type |
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<Code of the demand stratum> |
Scaling parameter lambda for each node of the decision tree They must become greater from top to bottom within the choice model structure, i.e. at a node, the scaling parameter must be at least as great as the scaling parameter of the overlying node in the model structure. |
11. Execute the procedure (Executing procedures in the procedure sequence).
The distribution of the demand is calculated using Nested demand. The calculation results are saved in the result demand matrices of the zones.
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Note: You can display the results in zone lists or in the network graphics (Displaying data graphically and in lists). |
