Noise is a major problem in big cities. The main source is ordinary traffic with cars, trains and airplanes that comply with international standards on noise emission. A good acoustic environmen in urban areas would demand L_DEN<40-45 dB. Present levels are frequently above 65 or 70. Therefore, it has been a great difficulty to formulate noise immission standards. L_DEN<55 dB was set as goal in some countries in northern Europe already two or three decades ago. It corresponds to a situation where some 5 percent or so of the population is highly annoyed so it is not a satisfactory goal from the health point of view. Nevertheless, L_DEN<55 dB in all residential areas is without reach during a foreseeable time period.
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