A model for computing environmental noise levels due to motor vehicle traffic in Visakhapatnam city

Apphed Acousttcs 27 (! 989) 129-136

A Model for Computing Environmental Noise Levels due to Motor Vehicle Traffic in Visakhapatnam City M G S e s h a g m Rao, P R a m a h n g e s w a r a Rao, K. S n m v a s Dev & K Venkateswara Rao Department of Engmeenng Physics, College of Engmeermg, Andhra Umverslty, Vlsakhapatnam--530 003, Indm (Recewed 16 August 1988, revised versmn recewed 23 December 1988, accepted 4 January 1989)

ABSTRACT Semt-empmcal equanons for predtctmg norse levels m the dtfferent zones of Vzsakhapatnam city have been developed from extenswe measurement of norse levels and tra~c denstttes m dtfferent zones of the ctty (65 pomts covering four zones of the city) The agreement between the predtcted and expertmental values ts wtthm ±5 dB(A)

INTRODUCTION In urban areas the major contribution to the environmental no~se levels is due to motor vehicular traffic In a c~ty with reasonably large traffic actwlty, the ambient levels reach very high values, necessitating the planning of noise control methods by controlling the density of the flow of motor vehicles The ambient no~se levels m most of the localmes of Visakhapatnam city, which is undergoing urbamsatmn and mdustnahsatmn at a phenomenal rate, are well above the desirable levels adopted by many countries The motor vehicular traffic m Indian crees, unhke that in many Western countries, IS complex, consisting of many types of motor vehicles each emitting a distinctly different average noise level. The ambient noise level is distinctly a function of the traffic density, besides being dependent on such factors as speeds of these vehicles, width of the road, and the presence or 129 Apphed Acoust,cs 0003-682X/89/$03 50 © 1989 Elsevier Scaence Pubhshers Ltd, England Pnnted m Great Britain

130 M G Seshagtrl Rao, P Ramahngeswara Rao, K Srmtvas Dev, K Venkateswara Rao absence of reflecting and absorbing surfaces on the sides of roads such as buildings and trees As such, a mathematical relationship can be worked out connecting the overall noise level In the environment and the motor vehicle density contributing to the noise level The environmental noise level is generally indicated by the eqmvalent continuous noise level L~q A number o f studies have been carried out 1 -10 on the noise made by individual motor vehicles of different types, and o f the overall noise in the environment A few of them have tried mathematical models to predict the ambient noise levels from the vehicle density However, all these studies have originated from the USA, Canada and Western Europe, where the roads are good and of standard widths and also the motor vehicle categories are few, and in each category the ages and c o n d m o n of the vehicles are confined to a narrow band Further, the average noise levels emitted by each of the categories of vehicles have been evaluated in these cases from measurements made on these individual vehicles on standard test sites, except in the case of Ref 4 Studies on noise levels (kerbslde values) emitted by seven distinctly different categories of motor vehicles plying on the roads of VIsakhapatnam city under actual c o n d m o n s have been carried out 11 and the average Lmax values have been esUmated The same study has also shown that the average noise level of a particular type o f vehicle is quite insensitive (within 4-_1 dB(A)) to factors such as road width, the c o n d m o n o f the road surface and the presence or absence of reflecting and absorbing surfaces. As the average speed with which the vehicles move on the inner city roads rarely exceeds 2 5 - 3 0 k m / h and as the noise emission levels of the different categories of motor vehicles rarely changed by more than + 1 dB(A) In this speed range, it is assumed that the environmental noise level due to m o t o r vehicular traffic to a first approximation is a function of the traffic volume only Accordingly an empirical relation connecting the L~q level and the traffic density is proposed, Its validity is tested by using the extensive data o f enwronmental noise levels (Le~ values for each hour) measured over the entire city, and the m o t o r vehicular traffic density existing during this period, whlch has also been measured

METHOD OF CALCULATION AND MEASUREMENT Noise levels (Le~ values) for the city have been measured by choosing 65 locations spread over the entire area The measurements were made throughout the entire period m a day when there was reasonable traffic activity, m general from 0800 to 2100. Le~ values in dB(A) for each h o u r have been recorded using sound level meters of type CEL 193 (an IEC-651,

Norse level model for motor vehtcle traffic

131

BS5969 Type I Instrument) and CEL283 (an IEC-651, BS5969 Type II Instrument), using an A-weighting network The sound level meter is mounted on a stand at a helght of 1 2 m above ground level and is located at the side of the road as per ISO Regulations During the same period each hour the motor vehicle density is also evaluated by counting the number of motor vehicles (for a period of 20-30 mm in each hour) for each type that crosses the point of measurement m either direction on the road Different zones of the o t y are classified as residential, commercial, residential cum commercial, and industrial, depending on the use to which the area is subjected The mean noise levels (Lmax)mea.,emitted by the seven categories of motor vehicles on the roads of Visakhapatnam have been determined m previous work 11 by studying a total of 4994 vehicles From this study the eqmvalent number of vehicles of a particular category whose total noise emission level equals that of a single vehicle of another category can be computed Thus the total traffic density consisting of the different types of vehicles can be converted to an equivalent density of a particular category Le., the eqmvalent continuous level at a particular place, can be expressed in the form of an equation Leq = C + Klog Nx where C and K are constants whde Nx is the eqmvalent number of vehicles per hour of a particular category corresponding to the total mixed traffic density A plot of Leq measured against the logarithm of the eqmvalent number of vehicles of a particular category should be a straight hne, and once C and K are evaluated from this equation, a measurement of the traffic density enables one to compute the L,~

RESULTS A N D DISCUSSION Table 1 presents the 'Mean Noise Levels' emitted by different categories of vehicles on the roads of the city and the eqmvalent number of hght vehicles (scooters) and the equivalent number of heavy vehicles (trucks) m terms of the average noise emission levels It can be seen from the table that scooters (hght vehicles) with a mean emission level of 73 20 dB(A) are the least noisy vehicles, while trucks (heavy vehicles) with a mean emission level of 87 42 dB(A) are the noisiest vehicles The hourly traffic density at each of the 65 locations studied is converted into the equivalent number of light vehicles per hour and the eqmvalent number of heavy vehicles per hour using the conversion factors from Table 1 The logarithms of these equivalent traffic densities for each hour for

132

M G Seshagtrt Rao, P Ramahngeswara Rao, K Srmwas Dev, K Venkateswara Rao TABLE 1 L . . . . Values for Different Categories of Vehicles and Conversion Factors for Eqmvalent Numbers of Light Vehicles (Scooters) and Heavy Vehicles (Trucks)

SI No

1 2 3 4 5 6 7

Category of vehwles Scooters Mopeds Tempos a Motor cycles Cars Buses Trucks

L .... value (dB(A)) 73 23 74 30 76 28 78 43 79 28 86 00 87 42

Equwalent Equwalent number of number of scooters trucks 10 12 20 33 4 03 18 9 26 2

0 038 0 048 0 073 0 126 0 153 0 714 1 000

a Three-wheeled automobile used m Indmn cities

different zones (i e residential, commercial, residential cum commercial, and industrial) are plotted against the corresponding hourly Leq values The plots are fitted to average straight lines which can be represented by the equation Leq = C + Klog Nx where Nx is the eqmvalent number of heavy or hght vehicles per hour These plots for the different types of locations are shown m Figs 1 and 2 for equivalent numbers of heavy vehicles and light vehicles respectwely Though the scatter of points looks wide, it can be seen from the figures that almost all the points lie within the ___5 dB(A) range from the straight line Figure 3 represents the same plot for equivalent light and heavy vehicles for all the locations in the city combined Values of C and K for all these locations and types of vehicles have been computed and Table 2 presents these values A look at Table 2 shows that the value of C is almost the same for all except the commercial zone which has a slightly higher value C represents the general background noise level in the absence of all vehicular traffic actwlty and this has a value around 40 dB(A) for all the zones except the commercial zone which has a value around 44 0 dB(A) for hght vehicles and 490dB(A) for heavy vehicles The higher background level for the commercial zone can be justified as the commercial actlwty in the zone raises the background level In all the zones and for the entire city, the K value obtained with equivalent heavy vehicle density Is higher than that obtained with eqmvalent hght vehicle density From the distnbuUon of points it can be seen that the equations for Leq

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133

obtained for the ent]re cnty are less accurate for prednct~on purposes compared to those for the mdw~dual zones where all the pomts more or less he w~thm the + 5 dB(A) zone As such it is desirable that equations for the lndw~dual zones be used for prediction purposes, If the nature o f the zone ~s known These equations enable an easy and qmck prediction o f the ambient noise levels, ff the traffic density is determined by counting the numbers and types RESIDENTIAL

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M G Seshagut Rao, P Ramahngeswara Rao, K Srmwas Dev, K Venkateswara Rao

134

of different vehicles that ply on the road m a particular locahty However, the accuracy of these pred]ct]ons is +5dB(A), though m many practical situations the devlat]on from the actual value may be even less The equations presented here are semn-emplrlcal For better predlctmns the contribution to L~q from the speeds of all the individual vehicles, the road condmons and the enwronmental background should also be taken into consideration In the present study we have justifiably ignored their contribution, as vehicle speeds m the city rarely exceeded 30 km/h and other conditions contributed less than __+1 dB(A) to the ambient sound level RESIDENTIAL

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TABLE 2 Values o f C and K for Different Zones and for All Zones Combined

SI No 1 2 3 4 5 6 7 8 9 10

Zone

All zones (combined) All zones (combined) Residential ResldenUal Commercial Commercial Residential cum commercial Residential cum commercial Industrial Industrial

Category (vehwles) Heavy Light Heavy Light Heavy Light Heavy Light Heavy Light

C (dB(A)) 44 41 41 41 49 43 40 41 40 40

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K

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136 M G Seshaglrt Rao, P Ramahngeswara Rao, K Srmwas Dev, K Venkateswara Rao Thus to a first approximation the relationships presented here afford quick prediction of the ambient noxse levels within ___5 dB(A)

ACKNOWLEDGEMENT The authors record their grateful thanks to the Mlmstry of Environment and Forests, Government of India, N e w Delhi, for finanoal assistance to a project of which the present work forms a part

REFERENCES 1 Cannelh, C B, Gluck, K & Santobom, S, A mathematical model for evaluation and prediction of the mean energy level of traffic noise m Italian towns Acoust, 53 (1983) 31 2 Balagopal Prabhu, T S & Muni Chakravarty, R L, A field survey of motor vehicle noise J Acoust Soc lndta, 6(2) (1978) 28 3 0 l s o n , N , Nozse pollutton o f the urban envtronment The problem as tt exists NRC Report, National Research Councd of Canada, Ottawa, Canada K1A 0S1, 1970 4 Lewis, P T, The noise generated by single vehicles m freely flowing traffic J Sound Vtb , 30 (1973) 191 5 Langdon, F J & Buller, I B, Noise nmsance caused by road traffic in residential areas, Part I J Sound Vzb, 47(2) (1976) 243 6 Myncec, H & Cop, A, Study of traffic nozse m etttes and resulting annoyance for the populanon Ministry of Public Health and Family Affairs, Department of Environmental Pollution, Belgium, 1977 7 Vallet, M, Maurm, M, Page, M A, Favre, B & Pachlaudl, G , Annoyance from and habituation to road traffic noise from urban express ways J Sound Vtb, 60(3) (1978) 423 8 0 l s o n , N, Survey of motor vehicle noise J Aeoust Soe A m e r , 52 (1972) 1291 9 Favre, B M, Noise emission of road vehicles Evaluation of some simple models J Sound Vzb, 91(4) (1983) 571 10 Thlessen, G J, Commumty no,se--Ground transportation National Research Council of Canada, Ottawa, Canada KIA 0S1, 1970 11 Seshagm Rao, M G & Ramahngeswara Rao, P, Study of noise levels emitted by mdlwdual motor vehicles on the roads of VIsakhapatnam city J Sound Vlb, 127 (1988) 65