Skip to content

Road with parallel Barrier

Often parallel barriers are used to reduce thee sound impact by roads. Those barriers can easily be generated in CadnaA by the command Parallel Object.

Entering a Road

Configuration| Reflection

When calculating the receiving levels at buildings façades the „Distance Points-Facade“ on dialog Object Snap is related to the minimum distance receiver-reflector as specified on the configuration-tab „Reflection“ (Calculation|Configuration menu).

With the receiver distance from the facade is smaller than the minimum distance receiver-reflector, no reflection by the own building is considered on the level at this receiver point. Keep this setting on the configurations for the time being.

Placing Receivers

  • Deactivate the option "Generates Rays (as Aux. Polygons)“ on the lower part of the dialog Receiver of the receiver in the default file.
  • Select the object "Receiver" from the toolbox and click once on the road side of each building located North of the road. The default height of the receivers is 4 meters.

  • Recalculate clicking the pocket calculator symbol .

  • Zoom-in () and measure using an auxiliary polygon () to check for the distance of the receivers 0.05 m in front of the façades.

Receivers attached to building facades

In a next step, the receiver levels shall be displayed in labels near to each receiver:

  • Switch to edit mode () and click with the mouse into the white area of the screen and select from the command Modify Objects from the context menu.

  • Select "Generate Label“ as action and as object type "Receiver".

  • Click OK and select on dialog Generate Label from list box „Attribute“ the attribute "LP1".
  • After clicking OK and confirming by „All“ the level LP1 (daytime value) will displayed in text boxes to the right of the receiver points.

In the next step, stations are defined alongside of the road to be used as reference when entering the barrier.

Generate Stations

  • Click with the right mouse button on the road’s axis and select from the context menu the command Generate Station.
  • Enter as the distance of stations 20 m to the right of the road (seen from first to last point).

  • Click on OK: Station marks are generated in steps of 20 m on the right of the road.

Parallel Object: Barrier

In the next step a parallel barrier is placed for a defined range of stations on the left side of the road.

  • Click with the right mouse button on the road’s axis and select the command Parallel Object from the context menu.
  • Enter distance of 5 m to the left of the road’s axis and a barrier height (height offset) on the dialog of 4 m.
  • Activate the option "Station Range" and enter - depending on the geometry in your example - a range „from...to“. " of ... till ", which protects the receiver points with a lateral additional width which will screen the receiver point from the road’s emission.

Parallel Object with Station Range (example)

  • By using an auxiliary polygon () you may check that the barrier was actually generated at a distance of 5 m from the road axis.

  • Start the calculation by a click on the pocket calculator symbol. The sound levels displayed by the labels will be updated.

Receiver levels at building facades with a road-parallel barrier

Calculating the Grid

In order to visualize the screening effect by the barrier the horizontal grid is calculated.

  • Select the object "Calculation Area" (symbol: ) from the toolbox and draw a rectangle which includes the road and all buildings.

  • Enter on dialog Properties on the Grid menu a receiver spacing of 1 by 1 meter.

  • Start the grid calculation by the command Calc Grid in Grid menu.

Noise grid, Daytime (using progressive colors, see Grid|Appearance)

When moving the mouse across the grid, CadnaA displays the current A-weighted level on the status bar on the lower right (e.g. "L: 67.5dBA").

Choose level boxes

In order to display the level inside a label at arbitrary positions on the grid use the object "Level box".

  • Select the object "Level Box" (symbol ) from the toolbox.

  • Click within the grid area to arbitrary positions to show the actual sound level on a text box.

Note

When switching the performance parameter via the symbol bar from day (LP1) to night (LP2), the level boxes on the grid will display the night-time values while the level boxes at the facade receivers still display the daytime values. This is due to the fact that when generating the labels for the facade receivers the daytime value (LP1) was selected deliberately for display (action „Generate Label“).

Grid Arithmetics

Via grid arithmetics (Grid menu) a level difference grid can be generated showing the level difference without-with barrier to display the screening effect on screen.

For details check the chapter Grid Arithmetics in this introductory manual.