@ JMD – Thank you for a very useful report on your visit to Shrewton. Superficially, HE look to have been helpful, but the devil is in the detail.

Let’s take road noise for example. HE claim they have a measure of 72 dB on the current A303. They don’t say where this sound level was measured, under what road conditions how the sound varied by location, etc etc. But what does 72 decibels mean. First, a bit of background on decibels (dB).  The decibel is used to compare two power levels, with the dB difference being 10 times the logarithm of the ratio of the powers.  More specifically we use dB in sound to compare the sound intensity values (W/m2).  For example if one sound level was 1000 times another, that would be a 30 dB difference.

So, what does a 72 Db noise actually sound like? It can be compared to the following: Passenger car at 65 mph at 25 ft (77 dB); motorway at 50 ft from the road edge @ 10 a.m. (76 dB). Living room music (76 dB); radio or TV-audio, vacuum cleaner (70 dB). (Source IAC Acoustics)

The WHO recommendation is for 55DB (see here)

That equates to the noise of a quiet suburb, a conversation at home heard from 1 metre away. Large electrical transformers at 100 feet. and it’s around a quarter of the level of sound at 72dB.

What HE seem to have forgotten to mention is that there is a second, more recent WHO figure for noise at night of 40 dB (see here). That equates the noise level being that of being in a quiet Library, bird calls (44 dB); lowest limit of urban ambient sound. Funny they haven’t mentioned it.

They also say they haven’t really considered the weather. Really, as long ago as 2009, the Parliamentary Office of Science and Technology (POST) were saying that it should be considering weather in such assessments. So we might ask why HE are ignoring POST?

You can take every statement that HE have offered up in a similar forensic way and you are left with the inescapable view that they have neither collected, nor provided sufficient data of an appropriate quality to reasonably expect a thinking person to choose a preferred route on the basis of the evidence presented.