Table 1
RANGE OF NOISE LEVELS AT LOCATIONS IN WHICH TRAFFIC NOISE PREDOMINATES
Group
A
ہے
B
Location
Arterial roads with many heavy vehicles and buses (kerbside)
(i) Major roads with heavy traffic and buses (fi) Side roads within 15-20 yds of A or B
group roads
Side roads within 20-50 yds of heavy traffic routes
Noise climate (dBA)*
Day
Night
(8 am.—6 p.n.) | (1 a.m.--ɓ a.m,)
80-68
75-63
68-50 61-48
Percentage of
the total numbers of points measured Jolling in each group
4
12
70-60
54-44
17
65-57
52-44
19
C
(i) Main residential roads
(ii)
(iii) Courtyards of blocks of flats screened
from direct view of heavy traffic
D
Residential roads with local traffic only
E
(i) Minor roads
(ii) Gardens of houses with traffic routes more
than 100 yds distant
60-52
48-43
21
F
Parks, courtyards, gardens in residential areas well away from traffic routes
55-50
46–41
9
G
Places of few local noises and only very distant traffic noise
!
50--17
43-40
I
* The range of noise level recorded for 80% of the time
compressors and roadbreakers, have been measured and the Government Committee on the Problem of Noise
in its report * have suggested that
that the maximum noise level from such operations should be limited to 70 or 75 dB(A) at the nearest build- ing (this level itself depending on the ambient level of noise from traffic). Building design or planning cannot normally take into account such
temporary
Traffic noise, in so far as the actual level depends on the number and kind of vehicles, can also vary but it appears that reasonable predictions can be made in a number of situations.
sources.
Various figures can be used to identify the noise level from traffic. Noise of this kind varies both in intensity and with time and a single figure. such as the average level. would give no indication of the peak values or the number of times the peaks occur. One way of defining the noise level which is thought to be the most appropriate is to specify the range of noise levels covered for 80% of the time. The upper limit of the range is exceeded by the peak noises, but only for 10% of the time; similarly, the noise level falls
Noise Final Report. Committee on the Problem of Noise, H.M.S.O. Cud. 2050. 1963.
130
below the lower limit for 10% of the time.
Noise from traffic is, of course, the net effect of the noise from all the individual vehicles composing it. Although many vehicles are capable of producing very high levels of engine noise, it is the heavier com- mercial vehicles that normally cause most of the peak levels in towns. This is presumably because they have to accelerate at full throttle in in low gear more frequently, and this is the condition for maximum noise. Figure I shows a typical re- cord of noise levels measured in London. Table 1. taken from the results of a survey of noise in Lon- don in 1961-2. shows the noise climates to be expected in various locations where traffic is on the whole the predominant source.
In the groups with the higher noise level. A-C. it is virtually the only source heard by day and often also at night. In the lower groups, D-G. other noises are louder from time to time but traffic noise is still the most frequently heard.
The levels are expressed in dB(A). i.e. corresponding to the use of the 'A' scale on a sound level meter, since it is known that this is a mea- sure of loudness for many typical urban noises. This scale takes some
account of the subjective assessment of loudness by suitably attenuating the lower frequencies and slightly accentuating the higher frequencies.
The maximum noise level generat- ed by an individual vehicle when heard at the kerbside is of the order of 90 dB(A). This level may be ex- perienced in any location by the roadside, more frequently in groups A or B but nevertheless occasionally in the quieter groups.
Protection given by buildings
en-
Noise from external sources ters a building principally through the windows, since even when closed these offer less insulation than the rest of the structure. For most buildings the different facades are effectively in different noise climates, depending on the character of the roads which bound them. Siting the rooms most sensitive to noise on the quieter sides or facing an internal courtyard of a building is an ob vious advantage. There appears. for example, to be a reduction of 5-10 dB(A) in the noise level at the back of a house compared with the front facing to the road.
With tall blocks of flats or offices this advantage is not maintained. Height above ground does not in-
THE HONG KONG & FAR EAST BUII DER-VOLUME 18, NUMBER 4