The L dn measurements take into account noises and the time of day that the noises occur. L dn contour. If a residence or school falls inside the 65-dB contour, the airport may be required to pay for soundproofing or even purchase the property. Other, less strenuous rules apply to businesses and recreational areas. Trains Federal regulations also apply to trains.
Locomotives have strict requirements on their noise production.
Traffic Traffic noise has become a problem in fast-growing communities. Many cities have built noise barriers to lessen the impact of traffic noise on neighborhoods and schools. These noise barriers must be used with care because an improperly placed barrier could increase the noise rather than decrease it. Some communities have local noise ordinances that limit the sound level measured a given distance from a home or business. People or businesses found in violation of the noise ordinance are subject to fines and penalties.