NoiseMap Forums
NoiseMap Software => Hints and Tips => Topic started by: roger on October 04, 2013, 04:28:00 PM
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The definition of Basic Noise Level (BNL) in DMRB is as follows:
“The BNL is a measure of source noise at a reference distance of 10 m from the nearside carriageway edge. It is determined from obtaining the estimated noise level from the 18 hour flow and then applying correction for vehicle speed, percentage of heavy vehicles, gradient and road surface as described in CRTN”.
This is slightly different from CRTN, which defines BNL as only the first part of the above, ie only the component due to the 18-hour total flow. It is also slightly different from the value displayed in NoiseMap RoadNoise, which is the 18-hour flow corrected for vehicle speed and percentage heavies.
But you can readily get the DMRB version of BNL from NoiseMap.
First, load the relevant scenario and select a receiver with a wide, unrestricted view of the road. Then go to Calculate>selected receiver and choose CRTN calculations and One Line per segment output.
Switch to the Results Output Window and you will see a calculation listed for each road segment (Some will have angle of view or distance cut-off and you will need to choose a different receiver to get these results).
In the middle of the page, you will see a heading BASIC NOISE LEVEL. The value printed in this column is the noise level for the 18-hour flow corrected for speed and percentage heavies. NOTE - the speed is the traffic speed after correction for the effect of gradient. The amount of speed change is shown under the heading SPD CHNG.
To get the value called BNL by DMRB, you need to add to the Basic Noise Level column the amounts show for low flow correction, surface correction and gradient correction in the next 3 columns.
Because the DMRB definition of BNL includes gradient and surface corrections, it may vary along a road even when the flow parameters don't change.
If you have any problem finding the numbered segments on the graphical map, remember that you can use the Edit>Find function (Ctrl+F) to locate any segment. Coose Road Segments under Find Object, and ID number under parameter and type the segment number in the box labelled Search String and then click Select First.
The selected segment will be highlighted and Selected Properties window with show its parameters, including the flow ID and name.