This report gives an analysis of measurements made of the acoustic performance of both single and dual barriers erected alongside the M6 where the motorway is elevated and runs close to an estate of 2-storey dwellings. With the barriers erected to a height of 3 metres the measured reductions in l10 at the facades of dwellings within 50-100 metres of the motorway ranged between 5-9 db(a) at first floor windows. The analysis confirms that barriers reduce the variability of the noise levels and indicates that sound reflections from single barriers do not cause a measurable increase in the noise levels on the opposite side of the motorway. Multiple reflections of sound between the dual barriers did not lead to any significant increase in the noise levels at the measurement positions. Values of the l10 (18-hour) behind the barriers were predicted using the procedure given in the doe publication 'design bulletin 26' and the more recent doe publication 'calculation of road traffic noise'. For both methods the predicted values of the l10 (18-hour) agreed reasonably well with the measured levels. The predictions obtained using the newer method were more accurate than the predictions obtained using the older method and whereas design bulletin 26 predictions systematically over-predicted the measured values there was no evidence of a similar over or under prediction trend when using the new prediction method. (Author/publisher)
Abstract