Noise Pollution 435Table 22-2. Sample Traflic Noise Data and Calculations for Example 22.3Rank % of time equal to
Time (s) WA) no. or exceeded dB(A)
10
20
30
40
50
60
70
80
90
10071
75
70
78
80
84
76
74
75
74~ 1 2 3 4 5 6 7 8 91090
80
70
60
50
40
30
20
10
0~
70
71
74
74
75
75
76
78
80
84SL dB(A)Figure 22-9. Results from a survey of transient noise. The data (from Table 22-2) are
plotted as percent of time the SL is exceeded vs the SL, in dB(A).
One widely used parameter for gauging the perceived level of noise from transient
sources is the noise pollution level (NPL), which takes into account the irritation caused
by impulse noises. The NPL is defined as
(22.10)