Source: adapted from R. Tolley and B. Turton (1995) Transport Systems,
Policy and Planning: A Geographical Approach, Burnt Mill, Harlow
Essex: Longman Scientific & Technical, p. 279.
Noise Levels from Different Sources
The decibel is a unit of measure of the intensity of acoustic pressure.
0 db is barely perceivable by human beings while 120 db is considered
to be the threshold of pain. The decibel grows on a logarithmic scale,
which means that an increase of 10 db corresponds to an increase in
intensity by a factor of 10. The acoustic pressure of 120 db is thus
one million times the one at 0 db.
Measures are often given in db(A) or in Leq when a time period is
involved. The Leq is the average of noise exposure, often in db (A),
over a time period. It is often measured for the 6h00-22h00 period,
which correspond to the period of the day when most activities are performed.
Legal limits usually range between 50 db and 65 db in OECD countries.
For instance, a jet airplane produces a sound intensity of 120 db(A)
during take off, a heavily used urban road intersection 80 db, and 70
db is a common noise level near a highway.