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From http://slashdot.jp/articles/04/02/09/2135212.shtml?topic=70
Hyogo national highway office decided to install "Active Noise Controll" devices at highways in Hyogo. It generates an "antiphase" sound which cancels the noice of the vehicles and reduces the noice level. This reminds me of a short story "Silence Please" by Arthur Clarke in "The Tales From The White Hart".
Clarke's speculation on this century was quite accurate, except the emergence of HAL 9000 and space-stations :-)