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.