NPL Acoustics: Technical Guides - Calculation of Road Traffic Noise 1988

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Revision History

This model implements most of the procedure detailed in the Calculation of Road Traffic Noise (CRTN - ISBN 0 11 550847 3) issued by the Department of Transport in 1988. The aim has been to provide a basic platform for calculating road traffic noise levels for non-complex situations. The model is limited where for example; a separate calculation will be needed to take account of any complex arrangements of reflecting surfaces, as only a simple reflective correction is implemented here. Where consideration is to be given to situations where low traffic flows occur, it will be necessary to make specific reference to CRTN. In such cases, a further correction is generally needed, which is not implemented here. Copies of CRTN are available from The Stationery Office.

The results from this calculation method may now be converted to the new EU noise indices. Please see the DEFRA website for further information.

Stage 1 - Divide the road scheme into segments

Divide the road scheme into segments such that the variation of noise within the segment is small.

Stage 2 - Basic Noise Level

Calculate the basic noise level at a reference distance of 10m away from the nearside carriageway edge for each segment.

Time Period	Hourly L₁₀18 Hour L₁₀
Total Vehicle Flow	(Veh/Hour : Veh/18 Hour)
Speed	(km/h) - Estimated from the road class?
Heavy Vehicles	(%)
Gradient	(%) Upward flow
Road Surface
	dB(A)

Stage 3 - Propagation

Assess for each segment the noise level at the reception point taking into account distance attenuation and screening of the source line.

Distance d (From edge of NS Carriageway)	(metres)
Source/Receiver Height Difference h	(metres)

The view of the road IS obscured

The view of the road is NOT obscured

	d_s
	h_s
	d_r
	h_r
	h_b

Absorbent Ground Cover
Average Path Height	(m)

dB(A)

Stage 4 - Site Layout

Correct the noise level at the reception point to take into account site layout features including reflections from buildings and facades, and the size of the source segment.

Include a correction for the receiver facade
Angle of View	(degrees)
Total angle of reflective surfaces (opposite)	(degrees)
	dB(A)

Corrections

If the road scheme contains low traffic flow (50 q 200 veh/h or 1000 Q 4000 veh/18-h day) then an additional correction may be required.

Low Traffic Flow Correction dB(A)

The total for this segment can now be calculated from those values above

dB(A)

Stage 5 - Combine contributions from all segments

Combine the contributions from all segments to give the predicted noise level at the reception point for the whole road scheme.

Add up all of the segment totals: the final number should be rounded to the nearest whole number (0.5 being rounded up). Also, remember that the screening and reflection corrections applied here are the simple ones defined by CRTN. Sections 34 and 35 of CRTN should be consulted where a more complex arrangement of reflective surfaces is to be considered.

The combined running total for all segments is calculated as described

Updated each time a segment total is calculated.

Segments

Predicted noise level dB(A)