Executive summary

The construction and physical properties of road surfaces have an influence on the level of tyre/road noise generated at the roadside.  Atkins Limited have reviewed recent studies concerning the acoustic performances of low noise surfaces from various countries, specifically Stone Mastic Asphalt (SMA) road surfaces, and current standards and methods for measuring their acoustic properties. 

SMA and Thin SMA (TSMA) pavements have relatively smooth driving surfaces due to the ‘stone skeleton’ created by the interlocking aggregate.  This creates a negative texture which provides voids for the air, trapped between the tyre and road surface, to dissipate, which in turn reduces ‘air pumping’ noise.  These attributes contribute to road surface noise reductions, which appear to be around 2 to 3 dB(A) in relation to HRA road surfaces of the same age.

TS2010 is a type of SMA that has been developed for use by Transport Scotland and a noise measurement study has recently been undertaken and reported by Transerv in 2018.  The Transerv report considers recently laid TS2010 and concludes that resurfacing an “aged carriageway with TS2010 will always yield a reduction [initial reduction] in overall traffic noise, at the sites in this study an average reduction of 4.5 dB(A) was found”.  Unfortunately, this figure is not a clear measure of the acoustic performance of TS2010, rather it is more a reflection of the various acoustic performances of the aged baseline road surfaces that were replaced by TS2010 in the Transerv study.

By making assumptions, based on the literature review, of the acoustic performance of TS2010 (-3dB(A)) and approximating a life span of 15 years, an initial review of selected Candidate Noise Management Areas showed positive results for the potential cost benefits of using TS2010 instead of HRA for periodic resurfacing of major roads.  Subject to further studies of TS2010’s actual acoustic performance.

Atkins recommends noise measurements are undertaken of the TS2010 road surface (approximately 12-18 months old) at two sites using the Statistical Pass-By method.  The benefits of using the Statistical Pass-By method are that a Road Surface Influence (RSI) value and an acoustic correction, bespoke to TS2010, can be calculated and more readily compared with other products.  The RSI value can then be used in to derive surface corrections, for both new road schemes and maintenance schemes, in accordance with the methodology of DMRB HD213/11.