Transportation Systems Simulation - A Tutorial for Multi-Modal Simulation Using VISSIM/Freeway: Calibration
After each simulation two files (.mer and .att) are generated. They can both be opened with Excel. The “.mer” file is a detailed record of every vehicles in the simulation. For this example, the “.att” file will be used.
Formatting Volume DataEdit
- Locate the “.att” file in the Evaluation output directory defined in the previous section.
- It will have the same name as your project, followed by the simulation number (001) and “Data Collection Measurements”
- If the file does not open with Excel by default, Right Click and select “Open with…” and choose Excel
- Once the file is open, locate the row with the text “$DATACOLLECTIONMEASUREMENT” (see Figure below)
- Delete all previous rows
- Select the entire “Column A” by moving your cursor and Clicking next to the letter “A” in the column header
- From the top Ribbon Select “Data” and “Text to Columns”
- A new “Convert Text to Columns Wizard” window will appear (see Figure below)
- Select “Delimited”
- Click Next
- Only Check the “Semicolon” box
- Click Finish
After adjusting column widths, the data should look very similar to the “Data Collection Measurement” window in VISSIM (see Figure below)
The following GEH (Geoffrey E. Havers) formula is the required method of determining an “Acceptable fit”. It requires the vehicles per hour (vph) from the VISSIM simulation (m) and the volumes (c) from PeMS. As the figure below indicates, GEH < 5.0 is acceptable. At least 85% of all freeway links (Mainlines, Off-Ramps and On-Ramps) must meet the criteria of GEH < 5.0.
The following Figure illustrates an example of GEH calculations using excel. The “GEH” column contains the required formula. Divided the number of GEH values above 5.0 by the total number of time intervals (36 or 24). This value should be less than 0.15 or 15%.
The following Figure shows a line chart that compares Observed traffic volumes (PeMS) and Simulation volumes (VISSIM). Note that lower GEH values will cause both lines to mimic and overlap.