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NoiseMap Software => Support => Topic started by: roger on June 26, 2013, 02:53:13 PM

Title: What are the DMRB 2008 additional procedures in the Calculation Options?
Post by: roger on June 26, 2013, 02:53:13 PM

There are four main additional procedures as follows, and these also apply to later editions of DMRB:

• Extrapolation beyond 300 m - NoiseMap normally extrapolates the hard and soft ground attenuation formulae however distant the receiver is.  DMRB 2008 states that the soft ground attenuation reaches a maximum magnitude at 600 m and this value should be used at greater receiver distances.
• Sound absorptive barriers - DMRB advises that barriers with a sound absorptive surface will have reduce reflection effects. It suggest that this should be estimated by removing the reflection correction, but that the real effect may not be this great.  NoiseMap will only remove the reflection effect of an absorptive barrier when the DMRB 2008 option is selected.   
• Reflection from opposite facades - CRTN does not apply any cut-off values beyond which reflections from opposite facades become insignificant.  NoiseMap allowed some control of this anomaly by allowing the user to set their own cut-off distance. The anomaly was recognised in DMRB 2008 and a formula was given to allow the user to calculate the cut-off distance from the geometry.  When DMRB 2008 is selected, NoiseMap performs this calculation and removes the reflection effect as appropriate.
• Road surface correction - additional advice was given in DMRB 2008 and 2011 in respect of low-noise surfaces.  The main change was that the road surface correction is to be applied where the traffic speed is at or above 75 kph, rather than at any speed, with a correction of -1 dB below 75 kph.  NoiseMap now provides an option to select a correction to be applied at or above 75 kph, and with this option, the correction at lower speeds is -1 dB(A).  This option  is always available and does not require the DMRB 2008 procedures to be invoked.