Highways Agency

The aim of the Scheme is to prevent any increase in noise wherever possible. Where this is not practicable then any increase in noise is limited, wherever possible, to 1 dB. It should be noted that noise changes of 1dB, either up or down, are not considered to be discernible to the human ear.

On completion of the widening the full width of motorway is surfaced with low noise surfacing. All existing noise barriers are retained and lengthened where necessary. Existing environmental barriers that are removed as a result of construction activities are replaced.

The provision of low noise surfacing and Environmental Barriers and improvements to existing barriers compensates for the noise effects of the additional traffic carried by the Scheme.

When the Scheme opens there will be a significant reduction in the number of people that might be bothered by noise. In the longer term 170 residential properties will  benefit from a reduction in noise levels of more than 1dB(A), of which 70 receive decreases of 2 – 3 dB(A) and 21 receive decreases of 3 - 6 dB(A).  125 properties receive an increase of between 1 and 2 dB(A). 

Four properties between Junctions 16 and 17 are expected to receive increased noise levels and qualify for Noise Insulation under Regulation 3 of the Noise Insulation Regulations 1975 (as amended 1988). These properties are at Alderbourne Cottage near Tatling End, Isle of Wight Farm near Gerrards Cross, and at Bircham Cottage and Four Acres in Heronsgate. No other properties qualify for noise insulation.

During the construction phase, noise control measures will be in place and the contractor will agree permissible noise levels with the local authority Environmental Health Officers.

Noise Survey Method

The Environmental Statement contains indicative noise contours based on noise calculations at a grid of 20 metres by 20 metres at a height of 4.5 metres above local ground to equate to first floor window heights. The contours represent free-field noise levels, i.e. they do not take account of facade reflection from individual properties. 

The detailed noise calculations were generated using a 3-D computer model in accordance with the procedure given in Calculation of Road Traffic Noise published in 1988 by the Department of Environment. This took account of:

• forecast 18-hour Average Annual Weekday Traffic (AAWT) traffic flows, including average speed and percentage of heavy vehicles;  
• road configuration such as the gradient, cutting and embankment heights and the road surface;
• ground topography, including distance of receiver from the road, angle of view, ground absorption and any natural and purpose built noise barriers. The effect of tree cover is discounted as they are not always in leaf.