Input and output attributes of assignment with ICA

Prior to the calculation of an assignment with ICA, certain attributes of network objects and also procedure parameters have to be set. After calculation, the results are available in the output attributes and can be displayed in the list view (Using Visum: Working with lists) or in the network editor (Using Visum: Specifying basic settings for the Network editor window).

An overview of all relevant input and output attributes for this procedure can be found under: ...\Program files\PTV Vision\PTV Visum 2025\Doc\Eng\AssignmentMethods.xls.

It is important that for those nodes whose turn impedances you want to calculate in detail using ICA, you select the Node impedance calculation (ICA) option for the Method for impedance at node attribute and set the Use preset method for impedance at node attribute to TRUE.

The following prerequisites are required for the assignment with ICA:

  • Prior to the assignment with ICA calculation, the geometry and control need to be modeled correctly for the nodes the ICA impedance calculation has been activated for. To check whether the calculation can be performed correctly for all nodes, from the Calculate menu, choose >Network check and check the Viability for ICA option.
  • For turns, the design volume PrT needs to be a volume attribute (Volume PrT with base volume [PCU]). Enter the settings via menu Calculate > General procedure settings > navigator entry PrT settings > Node impedances. For the design volume PrT, only factor 1.0 is permitted. This is due to the fact, that the calibration of the VDFs by turn would fail otherwise. The VD function used for turns is based on the hourly capacities output by ICA. This means that you can only perform assignment with ICA for assignment periods of 1h. As a result, hourly values for link and turn capacities must be defined.

For the output of results, the following options are provided:

There are different output variants: Primarily, the assignment with ICA fills the usual attributes of the various network object types (link, turn, etc.) with the calculated volumes and impedances. In addition to the common volume and travel time attributes, there are the following output attributes at (main) turns and links that are only filled through assignment with ICA:

Table 138: Additionally calculated turn/main turn attributes for assignment with ICA

Attribute

Meaning

Is ICA turn in ICA assignment

Indicates whether the ICA-Turn function is to be used for this turn in the assignment with ICA.

Final capacity for assignment with ICA

Corresponds to the smoothed capacity of the (main) turn determined by ICA, taking into account the minimum capacity from the procedure setting. The Capacity PrT attribute is not used for turns at (main) nodes calculated with ICA.

Final t0 for assignment with ICA

t0 that was recently used with ICA assignment. The t0 PrT attribute is not used for (main) turns at nodes calculated with ICA.

Final smoothed volume for assignment with ICA

Smoothed volume resulting from recent iteration.

tCur-PrTSys for assignment with ICA

tCur of the turn-specific VD function, including the final VD function parameters. In contrast, the attribute tCur-PrTSys stores the result calculated in the recent ICA calculation.

Final A for assignment with ICA

Final VD function parameter A for the turn-specific VDF

Final B for assignment with ICA

Final VD function parameter B for the turn-specific VDF

Suppressed upstream volume in assignment with ICA

Suppressed volume refers to the part of the volume that, according to blocking back calculation, is held back at bottlenecks upstream from the (main) turn and so does not reach it.

Table 139: Additionally calculated link attributes for assignment with ICA

Attribute

Meaning

Effective capacity for assignment with ICA

On uncongested links, effective capacity corresponds to link capacity or the Capacity PrT attribute. On congested links, it corresponds to the traffic volume exiting the link.

Suppressed upstream volume in assignment with ICA

Suppressed upstream volume refers to the part of the volume that, according to blocking back calculation, is held back at bottlenecks upstream from the (main) turn and so does not reach it.

Approach capacity of assignment with ICA

The value is only set for nodes of the control type Roundabout with the impedance model TRL/Kimber and acts as a mandatory limiting capacity in the blocking back calculation within assignment with ICA.

Furthermore, numerous diagnostic outputs are provided which can be used for convergence check. If the procedure converges either slowly or not at all, the outputs provide useful information, e.g. which turns show significant differences when calculated with ICA impedance calculation or the VD function.

  • As long as the procedure is running, you can watch the process in the "Goodness of PrT assignment with ICA" list.
  • *.csv files are created to which the program saves turn attribute data after each iteration. These files are helpful when you want to compare the development of attribute values of individual turns during the course of assignment with ICA.
  • The result attributes of the assignment with ICA for the analysis of the convergence behavior are stored in attributes of links, turns, main turns, and connectors. Which attributes are calculated at which network objects depends on the choice of convergence criteria. Attributes of connectors and links are calculated only if you use WebTAG-compliant convergence criteria. The calculated attributes of turns and main turns differ depending on whether the classic or WebTAG-compliant convergence criteria are used.
  • Optionally, an Excel report is created which contains the results of the recent ICA calculation. From the report it is to be seen, which volumes were used for the calculation and which capacities resulted from that. For nodes of the all-way stop type, the v/c value is output the same way as for nodes of the two-way stop type.

The precise times when attribute data is stored in an iteration are listed here (The procedure of assignment with ICA).