Noise is often defined as 'unwanted sound'. The laws around noise make it clear that sound only becomes noise when it exists in the wrong place or at the wrong time - causing annoyance, sleep disturbance or other effects. Airports in more densely populated areas are therefore considered to have a greater noise impact as a greater number of people are likely to be affected.
The effects of noise
The Department for Transport (DfT) commissioned a Survey of Noise Attitudes in 2014 to address emerging evidence that annoyance arising from aircraft noise had been increasing, building on the earlier noise surveys. This research study obtained new evidence on attitudes to aviation noise around airports in England and how they relate to UK aircraft noise exposure indices.
The CAA's CAP 1506 describes the approach to the study, sampling strategy, determination of noise exposure, analytics approach and results. Ipsos MORI's technical report, Survey of Noise Attitudes, provides further information on the noise survey questionnaire, the selection and sampling process, response rates, participant demographics and survey resources. The raw data (Excel file) is available for review, which includes a data dictionary describing each question and guidance on decoding responses.
Finally, an independent peer review of the survey's analysis and final report was commissioned by the DfT and undertaken by Dr Hannah Devine-Wright (Placewise Ltd) and Stephen Turner (Stephen Turner Acoustics Ltd).
The same aircraft taking off may have a very different effect on different people, even in neighbouring houses. Both may detect it, but while one is undisturbed by it - perhaps because they have the television or radio on, or are simply accustomed to the noise - the other may find it highly annoying.
From a noise control perspective what matters is the cause of the annoyance. If it is the presence of the noise itself that produces direct and immediate annoyance, then reducing its level might do little to change the reaction. On the other hand, if annoyance is related to the intensity of the noise, then reducing it would help.
Some airports are located in areas of dense population and surrounded by major roads - even without aviation, they'd still be noise places. Other airports are in more tranquil areas, or extend into rural or semi-rural areas, which means a lower level of noise can have a greater impact on quality of life and well-being.
Protecting areas of tranquillity is recognised as important for society as a whole, so the effect of noise on a tranquil area can impact planning decisions about airport location and expansion, new runways and flight paths.
Many people feel that a quiet environment is needed for tasks that depend on being able to hear information, especially those involving mental concentration and creative activity. In particular, high levels of noise could be seen as very disruptive for children learning at school.
Many studies have sought to investigate this effect, and there is a growing body of evidence to suggest that exposure to high levels of noise can affect a child's reading ability, essentially because it disrupts their concentration.
It's well known that noise can interfere with sleep - that's why alarm clocks work! However, it's also possible to become accustomed to high levels of noise and so sleep through them, such as when you sleep on a plane or train.
It's also not just the volume of a noise that affects sleep - parents may well be woken by the stirring of a child, yet sleep through a thunderstorm. Sleep disturbance can also be caused by many factors other than noise, like stress, changes in light and other physiological reasons.
Despite extensive studies into the effects of noise on sleep, it is difficult to derive definitive noise exposure criteria governing sleep disturbance. What is clear, however, is that sleep disturbance is a significant cause of annoyance; so whether directly caused by noise or not, if people perceive a noise to be the reason for disturbed sleep they are more likely to be annoyed by it.
The level of aircraft noise experienced at locations beyond airport boundaries is not likely to cause hearing damage.
One of the effects of noise that is hardest to assess is stress. It is known that noise can cause a variety of biological reflexes and responses, which are referred to as stress reactions. However, it is unclear to what extent these might lead to clinically recognisable disease following a period of exposure to noise.
There seems to be general consensus that environmental noise can affect subjective sleep quality and mood the next day, and has an acute impact on heart rate. Some studies have found that children who are chronically exposed to noise experience raised levels of stress, increased blood pressure and mental health effects; but overall, scientific literature to date has generally found that the evidence for long-term impacts on stress hormone levels is inconclusive.