FHWA Traffic Noise Model FAQs

This following are frequently asked questions (FAQs) about the FHWA TNM information. The FAQs apply to all versions of TNM, unless specified. This information is current as of April 2004.

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Menu: Setup

General

1. Why can't I register coordinates of zero?

   You must type in a 0 even if the default display shows 0.00.

2. What are the setup defaults for TNM?

   TNM has built in default values for every parameter of every input type. For newly created TNM runs, the following are
   default values:
   Setup, General
   Input and display units: Metric
   Traffic entry type: LAeq1h Hourly
   Relative Humidity: 50%
   Temp. (deg C): 20 degrees
   Default ground type: Lawn
   Line of sight check, subsource height (m): 3.5
   Distance limit (m): 150

   Roadways
   Roadway width 3.66 m.
   Pavement type: Average
   Speed constraint 0.0: km/hr
   Vehicles affected: 100
   Control Device: none

   Receivers
   Dwelling Units: 1
   Height Above Ground: 4.92 ft (1.5 m)
   Existing Level (dBA): 0.00
   Noise Reduction Goal (dB): 8.00
   Impact Criteria Level (dBA): 66
   Substantial Increase (dB): 10
   (However, for converted TNM 1.0b runs brought into TNM 2.0 or later, the Noise Reduction Goal, Impact Criteria Level , and Substantial Increase defaults are set to zero)

   Barriers
   Type: Wall
   Pert. Increment: 0
   # Pert. Up:0
   # Pert Down: 0
   Height (m): 0
   Min. Height (m): 0
   Max Height (m): 30.48
   Cost ($/sq m): 0
   Additional Cost ($/sq m): 0
   NRC Lside: 0
   NRC Rside: 0

   Building Rows
   Avg. Height (m): 0
   Building Percentage (%): 20

   Ground Zones
   Type: Pavement
   Flow Resistivity (cgs Rayls): 20,000

   Tree Zones
   Avg. Height (m): 0.00

   Contour Zones
   Contour Tolerance (dB): 1
   Minimum Grid spacing (m): 60.96
   Grid height (m): 1.52

3. What kind of digitizer should I use with TNM?

   Any manufacturer/model that meets the LCS/Telegraphics Wintab Interface Specification (www.wintab.com), preferably with a 16-button puck (which offers more input functionality).

4. Why doesn't my digitizer work with TNM?

   You may want to check with your digitizer manufacturer www.pointing.com for their latest drivers. Also, there might be a conflict between WINTAB32.DLL files: TNM's installation program puts a copy of WINTAB32.DLL in directory TNM\PROGRAM on your hard disk. This version of WINTAB32.DLL works for some digitizers. Unfortunately, it sometimes interferes with other digitizers. If your digitizer does not work with TNM, then delete the file TNM\PROGRAM\WINTAB32.DLL. Be careful not to delete your own digitizer's version of WINTAB32.DLL, which will be in another directory depending upon your digitizer installation.

Register Plan

1. How do I enter Z coordinates while digitizing everything else?

   Enter Z coordinates as you digitize. Just after you click on a point to digitize its XY coordinates, press the "A" button on the digitizer puck. A Z-coordinate window is shown on the screen. Still at the digitizer, enter the point's Z coordinate with the puck numerals, 0 through 9. You must include two decimal digits. For example, to enter 120, press 12000. The value 120.00 will be displayed. If you pressed 120, only, 1.20 will be displayed. If needed, use the following digitizer puck buttons to edit the Z coordinate: "B" to backspace or "C" to clear. Press the "E" button to enter the coordinate. Then proceed to the next point. Receiver Z coordinates entered from the puck must be typed in with two extra 00s (e.g. 14.00). Users should also register widely spaced points, especially first and second points.

2. Is it recommended that I digitize Z coordinates?

   The intent for TNM was to allow you to digitize Z coordinates from paper highway profile sheets. To do so, you would need to register the profile sheets. However, TNM profile registration currently requires a 1:1 horizontal to vertical scale for profiles. All highway profiles have exaggerated vertical scales and, thus cannot be used for digitizing Z coordinates by TNM.

3. Why does TNM give me an accuracy warning when my coordinates are off by a small amount?

   While registering plan sheets, TNM computes the expected coordinates of the third point, and shows them in the Computed cells of the Verification box. If you decide that the computed and target coordinates are close enough, click OK. After you click OK, you receive a registration accuracy warning if the computed coordinates are off by more than 0.05 % (1.52 meters (5 ft.) in 3048 meters (10,000 ft.)). This warning is merely a guide; you may feel that a larger difference is acceptable.

4. Does TNM accept the default XY coordinates of zero when digitizing objects?

   If a coordinate is zero, you must re-enter it, even though it already appears entered as 0.00.