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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) Help on Traffic Flow
Speed (km/h) - Estimated from the road class?
Heavy Vehicles (%)
Gradient (%)  Upward flow Help on Gradient
Road Surface Help on Road Surface

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)
Help on distances
Cross section showing the distances required (click for further help)

The view of the road IS obscured The view of the road is NOT obscured
Barrier cross section showing the distances required ds
Absorbent Ground Cover
Average Path Height (m)

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)


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

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)