Night noise guidelines for Europe - WHO/Europe - World Health ...

GUIDELINES AND RECOMMENDATIONS 105
Secondly, the reactions per event are known in relation to levels at the ear of the
sleeper, so an assumption for an average insulation value must be made. In this
report a value of 21 dB (see Chapter 1, sections 1.3.4 and 1.3.5) has been selected.
This value is, however, subject to national and cultural differences. One thing
that stands out is the desire of a large part of the population to sleep with windows
(slightly) open. The relatively low value of 21 dB already takes this into
account. If noise levels increase, people do indeed close their windows, but obviously
reluctantly, as then complaints about bad air increase and sleep disturbance
remains high. This was already pointed out in the WHO guidelines on community
noise (WHO, 1999).
From source to source the number of separate events varies considerably. Road
traffic noise is characterized by relatively low levels per event and high numbers,
while air and rail traffic are characterized by high levels per event and low numbers.
For two typical situations estimates are made and presented in graphical
form. The first is an average urban road (600 motor vehicles per night, which corresponds
roughly to a 24-hour use of 8000 motor vehicles, or 3 million per year,
the lower boundary the END sets) and the second case is for an average situation
of air traffic exposure (8 flights per night, nearly 3000 per year).
Fig. 5.1 shows how effects increase with an increase of L night, outside values for the
typical road traffic situation (urban road ). A large number of events lead to high
levels of awakening once the threshold of L Amax, inside is exceeded. To illustrate
this in practical terms: values over 60 dB L night, outside occur at less then 5 metres
from the centre of the road.
In Fig. 5.2 the same graph is presented for the typical airport situation. Due to a
lower number of events there are fewer awakenings than in the road traffic case
(Fig. 5.1), but the same or more health effects.
In these examples the worst case figures can be factors higher: the maximum
number of awakenings for an L night, outside of 60–65 dB is around 300 per year.
A recent study suggests that high background levels (from motorways) with low
numbers of separate events can cause high levels of average motility (Passchier-
Vermeer, to be published). In Table 5.3 the full details are summarized.
5.4 DEALING WITH SITUATIONS EXCEEDING THE
THRESHOLDS
Noise exposure data demonstrate that a large part of the population is over the noeffect
levels. It is expected that this will extend into the future for quite some time.
This means that circumstances may require that a risk assessment must be made. It
is then recommended to apply the method laid out in Chapter 1, using the values
given in Tables 5.1 and 5.2 and the dose–effect relations given in Chapter 4.
Typical actions requiring risk assessment are:
• new infrastructure projects (if an environmental impact statement is required)
• improvement programmes
NIGHT NOISE GUIDELINES FOR EUROPE