Low down on quiet surfaces

This article summarises the work in TRL report PPR443 'A review on current research on road surface noise reduction techniques.' The report is intended to help local authorities and other transport stakeholders to make informed decisions about whether or not it is worthwhile looking at reduced noise road surfacing in their particular area. Modelling has shown that noise reductions of 1-4dB(A) can be achieved depending on traffic composition and mean speed for a range from 10-60km/h. As mean traffic speeds increase, higher reductions are estimated and found to be dependent on aggregate size, with reductions of 4, 5 and 6dB(A) as aggregate size decreases from 14 to 10 to 6mm at 110km/h. General problems with the durability of stone mastic asphalt surfacing are reported from Scotland. Transport Scotlandis developing a proprietary stone mastic asphalt surfacing material called TS2010, which has been refined to achieve the triple aims of being quiet, skidding resistant and durable. TS2010 contains a polymer modified binder and cellulose fibres which thicken the binder. Experience in the UK on the acoustic performance of low noise surfaces has shown that significant initial reductions in overall traffic noise can be achieved compared with hot rolled asphalt. The London Borough of Hillingdon achieved noise reductions of 6.6-7.5dB(A) when it used a textured thin asphalt for resurfacing on the A40. Research carried out in the UK and in other European countries demonstrates that the acoustic performance of all surface types deteriorates with age. However controlling noise at source has an effect wherever the road is within earshot whereas noise barriers tend to be very much more local in their effectiveness.