Calculating node impedances using Node impedance calculation (ICA)

VD functions are usually used to model volume-dependent travel times on links. They can also be used to model volume-dependent wait times for turns or complete nodes (Fundamentals: Intersection Capacity Analysis according to the Highway Capacity Manual (ICA)).

1.  For the nodes desired, specify the Node impedance calculation (ICA) method (Selecting the method for node impedance calculation).

2.  Make sure that at the nodes desired, the input attributes values are correct (Fundamentals: Intersection Capacity Analysis according to the Highway Capacity Manual (ICA)).

3.  From the Calculate menu, choose General procedure settings.

The General procedure settings window opens.

4.  In the navigator, select PrT settings > Node impedances > Node impedance calculation (ICA).

5.  Make the desired changes.

Element	Description
Treatment of U-turns	Treat U-turns as left-most left turn If this option is selected, U-turns are taken into account in the ICA calculation and treated as left-most left turns (in left-hand traffic as right-most right turns). The treatment of U-turns thus differs from HCM, where U-turns are not taken into account. Ignore U-turns If this option is selected, U-turns are not taken into account in the ICA calculation. For the rest of the node, the calculation is HCM-compliant. However, no values are calculated for U-turns.
Time interval	User-defined duration of the volume peak
Create Excel report	If this option has been checked, the ICA output is saved as a formatted Excel report *.xls. Notes The file is stored in the folder, that has been set for ICA files via project directories. The file name of the Excel report is generated automatically. ICA<Network file name>.xls for multiple nodes or ICA<Network file name>_<Node number>.xls for a single node. The output file includes an overview sheet and a special sheet for each node that stores the node's number and data. Another sheet stores error messages and warnings.

6.  For the nodes with various control types, adjust the settings via the navigator entry PrT settings > Impedances at node > Node impedance calculation (ICA):

• Signalized (Signalized nodes)
• Two-way stop (Two-way stop nodes)
• Roundabout (Roundabout)
• All-way stop (All-way stop)
• Uncontrolled (Uncontrolled nodes)

7.  Confirm with OK.

8.  Calculate the node impedances with an appropriate method (Methods for node impedance calculation).