M2 Widening Project - Noise barrier height

I found a really well prepared presentation on the noise problems associated with the proposed widening of the M2. A key element of the presentation covers the noise barriers, and in particular the height of them. The number of trucks using the M2 doubled in 2006 when the M7 opened. The report suggests some 47,000 cars and 7,300 trucks are using the M2 now, and the number of trucks is forecast to rise by 25% over the next ten years.
The noise barrier height is perhaps the critical factor in shielding the neighbourhood from the noise of these trucks, and the existing commonly used 2.4m high barriers are just inadequate. With truck exhausts typically 4.5m high, or more, those barriers achieve very little. A 4.8m barrier would seem to be essential.
Where the motorway is below the level of adjacent houses, such as where it crosses Chilworth Reserve, even higher barriers might be needed.
Of particular concern to residents must be the likelihood of the barriers being removed totally during periods of the two year construction program.