You can insert and edit VD functions and then allocate them to link types, nodes, or turns.
1. For the particular network object type, open the VDF selection window:
- Link types (Selecting VDFs for link types)
- Node types (Selecting VDFs for node types)
- Turn types (Selecting VDFs for turn types)
2. In the Volume-delay functions section, click the 
symbol.
The Volume-delay function parameters window opens.
3. Make the desired changes.
|
Element |
Description |
|
Number |
Freely selectable, unique number of the VD function Note Use this number to allocate the VDF to particular link types, node types, or turn types. |
|
Name |
Here you can enter an additional name or a description. |
|
Type |
In the list, click a VD function type (Fundamentals: Predefined VD functions). Note In addition to the predefined VDFs listed, you may also use your own VDF (Applying user-defined volume-delay functions). AKCELIK Wait times at nodes AKCELIK2 Speed reduction on links BPR Bureau of Public Roads function BPR2 Modified BPR function with a different parameter b for the saturated and the unsaturated state BPR3 Modified BPR function, for which an additional supplement d per vehicle can be specified in the saturated state. CONICAL (Spiess) CONICAL_MARGINAL A marginal-cost version of the CONICAL function, proposed by Spiess to calculate a system optimum instead of a user optimum in the Equilibrium assignment. EXPONENTIAL Models queuing at entry legs whose inflow is restricted by signal control (Ramp Metering) INRETS The INRETS function of the French Institut National de Recherche sur les Transports et leur Sécurité Constant A constant function where the capacity has no impact on the travel time (tcur = t0) LOGISTIC, QUADRATIC, SIGMOIDAL_MMF_NODES (Morgan-Mercer-Flodin), SIGMOIDAL_MMF_LINKS Functions for modeling turn impedances TMODEL_LINKS, TMODEL_NODES Specific TModel functions, (Fundamentals: Node impedance of nodes VD function) Lohse Modified BPR function with a linear rise in the congested section, according to the queuing theories Linear bottle-neck Linear bottle-neck modeling |
|
Function |
The selected function is displayed in this section. |
|
Parameters |
Enter the VDF parameters in the input fields. Note Next to VDF number and name in the list, the user-defined parameters will be displayed in alphabetical order in parentheses. Closed If this option has been checked, the particular network object will only be included in path search if no alternative path can be found (e.g. for residential traffic). In this case, Visum assigns a high virtual time penalty, which, for example, has to be considered in the travel time skim matrix, when evaluating path times. Hard closure If this option has been checked, the particular network object will be excluded from path search. Notes The option Hard closure is only visible if the option Closed has been selected. If network objects are blocked by a VDF please make sure, that the network remains consistent for OD pairs with demand > 0. If option Closed or Hard closure has been checked for a VDF, the particular entry Weak closure or Hard closure will be displayed next to the VDF number in the list. |
4. Edit the preset parameters, if applicable.
5. Confirm with OK.
The volume-delay function has been selected and together with the number, the name and the user-defined parameters is added to the list of Volume-delay functions.
6. If necessary, make further changes to the list of VD functions:
|
Element |
Description |
|
Use the symbol to edit the selected VD function. |
|
Use the symbol to remove the selected VD function from the list. As long as a VDF is still allocated to a link type, you may not remove it from the list. |
|
The symbol can be used to change the selection of attributes displayed in the VD functions list. |
