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Specifying Road Emission

The emission caused by the traffic of a road is characterized by its emission level. This value is calculated automatically according to the selected standard or guideline by CadnaA based on the road’s traffic data.

Configuration|tab Road

With the CNOSSOS-EU road noise calculation procedure the following default settings are used:

  • option „Calc exactly one Reflection Order“ OFF: In this case, the maximum order of reflection is specified via the „Reflection“ tab.
  • option „Calculate outer Lanes separately“ ON: The center lines of the outermost lanes of a road are the emission lines (at a height of 0.05 m). When this option is activated just the road’s center line represents the emission line.
  • option „Use Temperature from Industry-Tab“ OFF: In this case, the reference temperature is used (20 °C).
  • no studded tyres
  • Default Percentages: This specifies globally the percentage of class 3 in the sum 2+3, and the percentage of class 4b in the sum 4a+4b.
  • „Vehicle Classes“ and „Meteorology“: default settings

Road Emission & Emission Level

The emission parameter in CNOSSOS-EU is the A-weighted long-term average sound pressure level for Day, Evening and Night period, computed by summation over all frequencies (octaves from 125 to 4000 Hz).

There are three options to specify road emission data:

  1. entering MDTD (Mean Daily Traffic Data) and road type: Since road types are only defined for the Austrian interpretation of CNOSSOS-EU, those are used.

  2. entering „Exact Count Data“: specify number of vehicles per hour and percentages of vehicle classes. This is the default procedure in CNOSSOS-EU.

  3. specifying the emission level LwA‘ (=PWL‘) in dB(A) directly.

Entering MDTD

Though the MDTD is not an intrinsic feature of the European calculation method, it is used here for reasons of simplicity.

  • Select the object "Road" from the toolbox and enter a road running from the left to the right across the screen using the mouse (scale 1:1000).
  • Double-click on the road’s axis and enter a road width of 3 meters.
  • Select the road type „national“ and enter a MDTD of 20000 vehicles per day.
  • Select the road surface „CNS_01 Reference road surface“.

The emission level is calculated for periods Day, Evening and Night.

CNOSSOS-EU road emission based on MDTD-data

  • Close the dialog Road and select the receiver from the toolbox.
  • Place a receiver perpendicular to the road’s axis and - while still being in input mode - click on the receiver’s border with the right mouse button.

Generate Rays

  • Activate the option „Generate Rays (as Auxiliary Polygons)" on the bottom of the receiver’s dialog.
  • Start the calculation by click on the pocket calculator symbol on the tool bar.

Road and receiver with rays as auxiliary polygons

The figure indicates that the road as a line source is segmented into sections, each of which is replaced by a point source in calculation. This occurs for both emission lines separately.

  • Double-click at on the receiver to display the resulting levels.

Defining a Diurnal Pattern

Specifying the road emission based on a diurnal pattern requires to define such a pattern first.

  • Open the tables "Diurnal Pattern" on menu Tables|Libraries (local).
  • Insert a new line via the table’s context menu (right mouse button).
  • Double-click on the line to enter values.
  • Enter a name and ID for the diurnal pattern.
  • Make sure that application „Roads“ is selected.
  • Click with the right mouse button into the column "Veh/h" and select the command Change Column from the context menu. Enter for „Arithmetic“ as new value 1000 and click OK.
  • Proceed in the same way for the percentage of heavy goods vehicles (HGV) in column "HGV (%)" by entering 20 %.
  • Overwrite a section of the input value in the table (e.g. 6:00 h to 14:00 h) with 2000 vehicles/hour and with 8% for percentage HGV.

Diurnal pattern with hourly traffic data

Note

Diurnal patterns can be imported via the ODBC-interface in CadnaA. Refer to chapter ODBC-Import in this introductory manual.

  • Close the dialog with OK and then click on the button "Close" in order to close the table "Diurnal Pattern".
  • Double-click on the road and select from the list box „Road Type“ the user-defined diurnal variation "T1" from the end of the list.

Selecting the diurnal pattern on dialog Road, List box „Road Type“

Note

The traffic counts of the diurnal variation are used as defined if an MDTD of zero is entered. If a MDTD-value is entered, however, the hourly traffic data of the diurnal pattern is normalized according to: \(M_{verwendet} = DTV_{eingegeben} * \frac{M_{Tagesgang}}{DTV_{Tagesgang}}\)

Specifying Road Gradient

When entering a value into the list box "Road Gradient: Input (%)“ the corresponding gradient correction according to CNOSSOS-EU is considered. The correction applies to the entire road section. In particular, it is independent from diverging height information at individual polygon points - and subsequently gradients between those points - due to an existent terrain model.

Road Gradient auto

With selection "Road Gradient: auto“ the gradients of roads modeled from several sections are calculated automatically. In this case, the displayed emission level does not include the gradient correction (since it varies from section to section.) However, the correction is calculated and taken into account in the calculation of propagation for each road section separately.

On the list box "Gradient" the direction of traffic flow for the two outer lanes is specified. The arrows (or the abbreviations VA, AV, AA, and VV) refer to the traffic direction on the two lanes when looking from first to last point of the road.

Buildings along the road

In order to consider the reflections due to buildings at either sides of a road the buildings must have reflective properties and at least the first order of reflection has to be selected in the configuration.

  • Enter a building parallel to the road.

Note

If you do not recall the sequence of commands when entering multi-point objects, please check the chapter Inserting Objects using the Mouse in this manual.

  • Change to the edit mode and double-click on the building’s border.
  • Click the button „Geometry“ and enter a height of 10 m (relative).
  • Close the dialog with OK.

  • Select option „Reflection Loss“ and select via the selector the type „Smooth Facade/refl. Barrier“.

  • Close the Building dialog with OK.

The building has now reflective properties.

  • Duplicate the building by using the CTRL-key on your keyboard.

Note

To copy objects, please check the chapter Copying Objects in this manual.

Proceed in same way to place three buildings at each side of the road.

  • Delete the former receiver.
  • Finally, display the site as a wire frame model in 3D-view (command 3D-View on Options menu, setting „General Parallel“)

3D-View (Options menu): road with 6 buildings

  • Check the settings for the Object Snap (Options menu).
  • Set the „Snap Radius in Pixel“ to 10 and a „Distance Points-Facade“ of 0.05 m (5 centimeters).

  • Place a receiver of the road side of a building and open die Receiver dialog.
  • Check the option „Generate Rays (as Aux. Polygons)“ and clos ethe receiver dialog.
  • Open the configuration tab „Reflection“ and enter/select a reflection order of 1.
  • Calculate the receiver level by clicking the pocket calculator symbol .

Rays displayed for direct path and 1st order reflections.

  • Double-click on a ray to display the dialog.

The rays are displayed using Auxiliary Polygons. The ID shows information identifying the object as a ray with its level, on ray order and whether screened or not..

In this example, the rays transmits a partial level of 36.5 dB(A) - Daytime level - and is of 1st order, indicated by the string part „..._01“.

A screened ray would show an „s“ add at the end of the ID.

  • Save the file.