TRAFFIC NOISES

Evening Post, Volume CXIX, Issue 30, 5 February 1935, Page 5

TRAFFIC NOISES

SCIENTIST'S SURVEY "INTERFERENCE LEVELS" The scientific investigation and measurement of street traffic noises was outlined before the mathematics and physics section of the Science Congress at Melbourne by Mr. R. O. Cherry, wlio described graphs and the definition or an "interference level," which, he said, depended on the traffic normally expected in a street. A quiet street in the city might be "intolerably noisy" in a suburban residential area. Mr. Cherry said that in order to assess the noisiness of a street it was not enough merely to measure the peak" intensities of individual vehicles as they passed the point of observation. Even a ■ graph which showed the manner in which the noise varied from minute to minute did not, by itself, convey the information required to compare the noisiness of two places. In addition, the graph required elaborate' measuring . and recording apparatus for its delineation. The degree of noisiness of a street was really only a. question of the total time that the noise intensity exceeded some particular-value. This value, which could be called the ."interference level," depended on the' traffic normally expected in that street, and therefore varied with each locality. Thus, a quiet street in the city' would become intolerably noisy in a'suburban residential area. In order to determine the noise characteristic of a street, a series of observations .were taken, in which the time during which the noise intensity exceeded known values was measured. The results were shown in a curve, giving the relation between "noise intensity" and '"proportion of total time of observation that this intensity was exceeded." •■' • This curve had been called the total or cumulative noise curve, and the results' showed that each locality had its own particular type of curve. Thus a steep hill in the city,with a. moderate density of traffic had a different form of total noise curve to that of a leyel street with much greater traffic volume. These, total noise curves were, obtained with simple apparatus, and manual recording could be done by a single observer without, undue labour. Another advantage of • these total noise: curves was that, they showed at once the exact manner in which two localities could be compared as regards noisiness. As an example of this,- the curves obtained for several city streets on days when the electric and cable trams were not running were compared with those obtained •during normal operation of the. trams. This enabled an accurate assessment to be made of the noises due to these vehicles, and showed that in typical city streets they produced as much noise as the whole of the; rest of the traffic combined. Another important deduction from these, curves was that they allowed an, estimate to be;made of the "interference level" for. various city streets. Since the effect ot each vehicle on. the total noise curve had been determined, one was" now in a position of being able to suggest limits which the noise of any particular vehicle should not exceed.