NCHRP 255 (Post-processor for PrT assignments)

Note: This functionality is only available if the NCHRP 255 add-on is active ( Enabling or disabling add-ons).

This add-on uses a correction factor to correct turn volumes of links and turns in a forecast scenario (Fundamentals: NCHRP 255). The correction factor results from the differences between traffic counts and an assignment which describe the same time slice. This calculation is performed according to Report 255 (National Cooperative Highway Research Program).

1. On the toolbar, click Open Procedure sequence.

The Procedure sequence window opens.

2. Add the NCHRP 255 procedure of the Miscellaneous category to the given procedure sequence (Setting up and starting the procedure sequence).

3. Make sure that the inserted operation is marked and click the Edit button in the Operations section.

The NCHRP 255 Post Processor window opens.

4. Make the desired changes.

Element	Description
Active nodes only	If this option has been checked, flows passing passive nodes will not be adjusted
Adjustment procedure	Method for volume correction Difference Adjusted link volume = Future link assigned volume + (Link base count – Base link assigned volume) Average Link Adjusted Volume = Future Link Assigned Volume • (Difference + Ratio)/2 Ratio Link Adjusted Volume = Future Link Assigned Volume • (Link Base Count / Base Link Assigned Volume) Combination Due to the ratio between the counted turn volume and the assigned base volume, one of the methods mentioned above is used for calculation. Therefore, define - via Boundaries - the lower limit (0–1) and the upper limit (1–4). For values < lower limit, the Ratio method is used For values > lower limit and < upper limit, the Average method is used For values > upper limit, the Difference method is used
Boundaries	If method Combination has been selected for adjustment, you need to define the limits for the three methods.
Input data	Counted turn volume Via this button, select the numerical turn attribute that stores the counted turn data. Base Assigned Volume Via this button, select the numerical link attribute that stores basic assignment volume data. Future Assigned Volume Via this button, select the numerical link attribute that stores future assignment volume data.
Output data	Log file If this option has been checked, detailed information on the procedure run are logged to trace file. Adjusted link volume Link attribute, to which the corrected link volume is to be saved. Adjusted turn volume Turn attribute, to which the corrected turn volume is to be saved.

5. Confirm with OK.

6. Execute the procedure (Executing procedures in the procedure sequence).

The procedure is executed.