Assessment of Noise From Traffic on a Dual Carriageway

It has long been recognised that noise from road traffic can cause serious and unacceptable environmental disturbance.henceforth there has been almost simultaneous growth in the awareness to road traffic noise as a nuisance.The Wilson Committee reported these facts in I963.However little had been done about noise as a problem until the Land Compensation Act in l973.mainly because there was no recognised method of assessing the impact of road traffic noise and also because there was no statutory means of providing mitigation measures or compensation.The LCA was therefore a milestone in providing a legal framework and stipulating a method of assessment.The first quantitative method of traffic noise prediction was outlined in "New housing and road traffic noise'.This was soon followed by a very much improved and extensive procedure 'Calculation of Road Traffic Noise' (CRTN) which was published in 1975.The legal framework was contained in the Noise Insulation Regulations (NIR) published in 1975.which included the CRTN as the statutory method of predicting traffic noise.Use of the CRTN procedure over a number of years has highlighted a few shortcomings within it.Subsequently.this procedure was revised in 1988 and this revision took into account various additional factors.such as.the effect of low volume of traffic and the road surface texture.However.there remains a case of when to apply separate source lines for dual carriageways.This paper evaluates a situation that can affect a large number of nearby residents in an already sensitive area.it recommends that under certain conditions traffic noise should be calculated using two separate source lines.one for each carriageway.and the noise from each should then be combined to obtain the overall noise level.At present.this method is conditional upon firstly.the central reservation being greater than 5m in width or secondly.where the outer edges of the carriageway: are vertically separated by more than lm.Results of this evaluation shows that noise levels in certain areas are up to 3dB higher when calculated using two source lines.