It is hard to believe that the refined plan is not going to result in louder noise in Killiecrankie. That affects residents and visitors to the site, especially at the Memorial Cairn where an annual commemorative service is held. Throughout the year, people visit the area around the cairn as a focus for contemplation or remembrance. Commemoration is known to be an important part of respecting battlefields.

Earthworks offer noise attenuation. Jacobs says that the noise impact assessments that were made when the Environmental Statement was published will apply after huge changes are made to the amount of earthworks on the battlefield. The refinements will remove the replacement of a proposed bund (a mass of earth) that was created as noise mitigation when the original A9 was built. Instead of a noise-absorbent bund there will be 2 separate stone walls that reflect noise. The refinements will also remove the wide, earth embankments that were to run the length of the new road on the Memorial Cairn side.

Predicted noise levels are calculated by modelling. We had been told that the bund was included in the noise modelling when the Environmental Statement figures were published but it is impossible to estimate by how much the noise attenuation has been reduced now that the bund has been removed from the plan.

Low Noise Road Surface (LNRS) is the single most potent measure to mitigate noise in the scheme, according to Jacobs. The material is assumed to reduce surface noise by 3.5dB when vehicles are travelling at a speed of at least 47mph. Below that speed, the benefit is only 1dB. The expected benefit of switching to this surface will not be as great in the area of the Memorial Cairn as it will be elsewhere as LNRS is already in place from the far end of the Walled Garden at Urrard House (ch2298) to the Memorial Cairn field (ch2622) on both existing carriageways.

Noise predictions are complex. For the Environmental Statement, they were done in two stages. First, measurements were taken at 11 sample places in the entire stretch of road from Killiecrankie to Glen Garry. Four of these were in the Killiecrankie stretch. The noise measurements were fed into a model which predicted what the noise level would be at all buildings in the Killiecrankie to Glen Garry section in 2026, (the first year of operation) and in 2041 (15 years of operation).

From there, every other calculation follows. It is, therefore, essential that the model is trustworthy. To test it, a comparison was made of the measured noise levels at the 11 sample places with model-predicted noise levels. These would rarely be expected to coincide perfectly but Jacobs was happy that the results showed that “at nine of the locations there is a reasonably good correlation” of a difference of less than 2dB. In fact, only four of the 11 locations showed a difference of 2dB or less.

See the table

This does not appear to be a reasonably good correlation and raises questions about all noise impact assessments in the scheme. In the event that greater tolerance has to be built into the calculations, a change in the predicted range of noise that is expected in individual locations would be triggered. In other words, the Environmental Statement figures would need to change.

In the absence of evidence to prove that the noise impact assessments remain unchanged in spite of the removal of 50,000m3 worth of sound-absorbing material, it is hard to accept the claim. Without assurance that the noise modelling figures are as reliable as first thought, it is impossible.