I am not sure I can agree with Ian Walsh (Letters 15 July) that the advantages of thin surfacing - reduced noise and fuel consumption - far outweigh the disadvantages.
Noise levels measured by TRL on various surfaces show a reduction of about 1dB(A) for negatively textured stone mastic asphalt (SMA) and close graded macadam compared to hot rolled asphalt (HRA) - (101dB(A) at 80kph with 20mm aggregate). The only thing that stops these materials, including HRA, being considered as thin surfacing is the lack of a proprietary name. Noise is not a mandatory test for the achievement of BBA-HAPAS certification and even the previous 40mm maximum thickness limit has been removed.
The Highways Agency requires a 2.5dB(A) noise reduction for thin surfacings on trunk roads compared to HRA.
They have commissioned research on thin surfacings, including noise measurement. It would be interesting to know the results to date, including noise levels achieved and maintained. This would assist the current debate.
Having used a thin surfacing to achieve reduced noise, future maintenance by resurfacing with the same material is going to be significantly more expensive than the traditional surface dressing of HRA and close graded macadams - an increased cost that will be difficult to meet for the bulk of the local road network.
Frank Bedford (M), frank. bedford@ntlworld. com