Road traffic noise is everywhere growing in intensity, spreading to areas until now unaffected and creating as much concern as any other type of pollution. Surveys carried out in the UK, France, Norway, Japan and Sweden show not only that traffic is considered to generate the most annoying kind of noise, but that it is often one of the most serious problems that town-dwellers must face. The proportion of the population in the European Region exposed to high noise levels (equivalent to 65 dB over 24 hours) increased from 15% to 26% between 1980 and 1990. About 65% of the European population is estimated to be exposed to noise levels leading to serious annoyance, speech interference and sleep disturbance (55-65 dB over 24 hours). The world motor vehicle population (private cars and commercial vehicles) rose from 100 million units in 1960 to 200 million in 1970 and is thought to have exceeded 300 million units by 1980. In France, for example, it has been estimated that noise may have increased by an average 2-3 dB between 1970 and 1985. It can be concluded that as a result of the increase in road traffic, noise levels will increase unless preventive or corrective measures are taken. By the year 2000 the number of people exposed to noise exceeding 65 dB is expected to increase from 15% to 20%.