Iranian Journal of Environmental Health Science & Engineering,Vol. 3, No. 2, 2006, pp. 71-78

STUDY ON TRAFFIC NOISE LEVEL OF SYLHET BY MULTIPLE REGRESSION ANALYSIS ASSOCIATED WITH HEALTH HAZARDS

*¹J. B. Alam, ²M. Jobair Bin Alam, ³M. M. Rahman, ⁴A. K. Dikshit, ¹S. K. Khan

¹ Department of Civil and Environmental Engineering, Shahjalal University of Science and Technology, Sylhet
²Civil Engineering Department, Bangladesh University of Engineering and Technology
³Graduate Student, UTM, Mayalasia
⁴Indian Institute of Technology, Mumbai, India
*Corresponding author E-mail: jahiralam@yahoo.com, Tel/Fax: +0880 2911 4285

Received 11 November 2005; revised 7 Febuary 2006; accepted 12 March 2006

Code Number: se06011

ABSTRACT

INTRODUCTION

Noise is unacceptable level of sound that creates annoyance, hampers mental and physical peace, and may induce severe damage to the health. Along with the increasing degree of air and water pollution, noise pollution is also emerging as a new threat to the inhabitants of Sylhet City. Exposure to high level of noise may cause severe stress on the auditory and nervous system of the city dwellers, particularly the children. Motorized traffic is one of the major sources of noise pollution in urban areas. Frequent exposure to high level of noise hampers physical and mental peace and may cause damage to the health. Along with the increasing degree of air and water pollution, the inhabitants of Sylhet City are being exposed to high level of noise pollution. The level of noise pollution is very closely related with urbanization and motorization. Although there are many sources of noise, which include industries, construction works and indiscriminate use of loud speakers, motorized traffic is the principal source of creating noise in urban areas. During the 70s and early 80s, noise pollution was not a major concern for the dwellers of Sylhet City. With the increase of in the number of motorized vehicles in the city, the hazard of noise pollution has increased and exceeded the level of tolerance. Exposure to high level of noise causes severe stress on the auditory and nervous system. Das (2001) reported that the hearing ability of the inhabitants of the City has reduced during the last ten years. About five to seven percent of the patients admitted to the Sylhet Osmani Medical College are suffering from permanent deafness due to noise pollution (Ahmed, 1998). Disturbances created by noise may cause hypertension, headache, indigestion, peptic ulcer, pharyngitis, atherosclosis, bradycardia and ectopic beat (Papacostas and Prevedouros, 1993; Kadiyali, 1997). The paper aims at studying the level of noise pollution in Sylhet City and analyzing its level of severity. It analyses durinal variation of noise near the roadside and its relationship with traffic volume.

The paper also suggests several strategies to control the level of noise pollution in the city.

MATERIALS AND METHODS

Sound level, its frequency spectrum and its variation over time characterize noise. Although the level of noise largely depends on the subjective perception of the hearer about the loudness, the term sound level refers to a physical measure, which is a function of the magnitude of the pressure fluctuations. The most common measures of sound level are sound intensity and sound pressure. Sound intensity (also called sound power density) is the average rate of sound energy transmitted through a unit area perpendicular to the direction of sound propagation, typically measured in pico-watts per square meter. Since no instrument is available for directly measure the power level of a source, sound pressure is employed as a measure in this regard. Sound pressure is usually proportional to the square root of sound power. Because of dealing with large range of numbers, a logarithmic measure called decibel (dB) is used to describe sound level. The sound level in decibel is defined as follows,

where,

P = Root-mean-square sound pressure
(Newton per square meter)
P₀= Standard reference pressure corresponding to the weakest audible sound
(20 micronewton per square meter)

For practical purpose, the decibel scale ranges from zero, the threshold of hearing, to about 140 dB, the onset of pain. For every 10dB increase in sound level, the apparent loudness of sound doubles.

In order to account for the ear’s response to different levels of noise, weighing filters are used while measuring the sound level. The A-weighted sound level is devised to represent a person’s subjective response to the variation of sound more accurately. The A weighted sound level, measured in decibel (dBA), is the generally accepted scale for measuring sound level in transportation.

In this study, noise levels have been measured by Noise Meter (ELE, NL 04) at various locations from 7 am to 11 pm in four time intervals viz. 7 am-11 am; 11 am-3 pm; 3 pm-7 pm; and 7 pm to 11 pm from 2003 to 2004. Data collected was analyzed statistically to determine L₁₀, L₉₀, L_max, L_e, and L_aeq.

To determine the peoples’ willingness to obey law, the Logit model was employed. It is basically a regression model in which the dependent variable itself dichotomous in nature taking a 1 or 0 value. The logit model given by Alam (2006) is:

Where L_i is the log of odds ratio; L_i is called Logit, P_i is the probability of the peoples’ willingness to obey law, (1-P_i ) is the probability of not obeying law, P_i/(1-P_i) is odds ratio of people obeying law, X_i is independent variables, U_i is residual term, αis the interception, βi are the constants. The following Logit model was fitted t the data

L_i = In (P_i /(1-P_i) = α + βX +βX+βX +βX + U_i

Where, L_i =1 if the people willingness to obey lawand 0 if it is not.P_i = the probability of the people’s willingness toobey law.X₁ = Age of the respondent (yr)
X₂ = Experience of the respondent (yr)
X₃ = Educational qualification of the respondent
X₄ = Annual income of the respondents’ household
(Tk/household)

Study area and time

Noise levels have been measured at 37 locations in Sylhet City during 7 am to 11 pm of the workdays. The study incorporated all the major locations of the city, which included City Poly Clinic and Mother Care Clinic; Royal Hospital; Govt. Girls School; Blue Bird High School; Darshan Deuri Primary School; Jameya Islamic Madrasha, Pathantula; Ananda Niketon School; Dargah Gate Primary School; Police line School; Aziz medical center, Sylhet Govt. Pilot High School. Time-weighted average noise levels have been measured at the roadside as well as at distances away from the roadside. This was done to analyze the effects of distance and existing roadside barriers on the reduction of noise level. Daily traffic volume data was collected on the both direction count basis as per Road Materials and Standard Study Bangladesh (LGED, 1998) considering the following points:

• The survey site should provide good visibility of traffic.
• Proper shelter/safety should be provided to the staff.
• Any seasonal variation in traffic should be considered.

Traffic noise index was also calculated to measure annoyance responses to motor vehicle noise using the following formula:

TNI (dBA) = 4 × (L₁₀ - L₉₀) + (L₉₀ - 30) (dBA)

Where, L₁₀ and L₉₀ are the A-weighted decibel levels exceeded 10% and 90% of the time respectively (i.e. the peak and ambient levels respectively).

Fig. 1 shows the location of the sampling points inSylhet City (37 points).

Acceptable levels of noise

Various standards are being used in different countries regarding the acceptable levels of noise depending on the situation. Limits of acceptable noise level established by different organizations are given in Table 1. The study aimed at studying the level of noise pollution in Sylhet City and analyzing its level of severity. Moreover as most of the schools and hospitals, which are particularly vulnerable, are located near the roads, noise levels at these places at different distance have been determined in order to evaluate the safe distance. The study incorporated some of the schools and hospitals located near the roadside which include City Poly Clinic and Mother Care Clinic; Royal Hospital; Goverment. Girls High School; Blue Bird High School; Darshan Deuri Primary School; Pathantula Jameya Islamia Madrasha; Ananda Niketon School; Dargah Gate Primary School; Police line School; Aziz medical center, Sylhet Goverment.

RESULTS

From the Table 1, the five equations based on summation of X₁; X₁ X₂; X₁X₃ ; X₁X₄ are simultaneous solved to get the values of α, β, γand δ. The zero order, first order, second order and multiple correlation coefficients are calculated using SPSS software. Values of multiple regression coefficients indicate best correlation (as they lie between 0 and 1). Data of Table 3 has been used to predict the noise level at different distances near hospitals and educational institutions.

For L _eq X₁ = α + δ = 162.93; β = -32.20;

and γ= -3.49 R = 0.604

For L₉₀ X₁ = α + δ = 115.96; β = -20.552;

and γ = -6.017 R = 0.522

A comparison of predicted value from the equation and actual measured values of L₉₀ and L _eq are shown in Figs 1 and 2 for L₉₀ and L _eq respectively.

For L _eq; r₁₂ =0.2244; r₂₃ = 0.2187 and r₁₃ = -0.4931

For L₉₀; r₁₂ =0.2244; r₂₃ = 0.3906 and r₁₃ = -0.5209

Percentage of correlation for L₉₀ and L _eq are 52.2% and 60.4% respectively. A discrepancy between observed and predicted value is also given chi-square test. λ² are 0.9999 and 0.9999 for L₁₀; L₉₀ and L _eq , respectively.

For L _eq X₁ = α + δ* log20 = 45.25; β = 13.31;

and γ = 8.05 R = 0.561

For L₉₀ X₁ = α + δ *log 20 = 26.44; β = 9.972;

and γ = 7.80 R = 0.462

The above model was calibrated to estimate the effect of traffic flow, speed on noise. Using the model, noise level at a particular location as well as desirable positions for locating vulnerable institutions can be obtained. From the measured data from different sides of Sylhet, it is found that noise of density is not significantly affected by residential density. The noise level on the main road near residential area, hospital area and educational area were above the recommended level (65dBA). It was found from the Figs. 4 and 5 that the predictive equations are in 60-70% correlated with the measured noise level.

Sylhet city is becoming extremely crowded. The city area is endowed with educational institutes, residential areas, hotels, community centers, restaurants, banks, pharmacies, office building, health clinics, etc. but these have been developed in an unplanned way. This unplanned urbanization gave rise to severe environmental problems in the city area. The study suggests that vulnerable institutions (schools and hospitals) should be located about 60m away from the roadside unless any special arrangement to alleviate sound is used. Limitation of our prediction regressed equation is that this includes only three dependent traffic parameters- flow, mean speed and distance, which only provide one point on the cumulative time/level distribution, whereas by considering actual computer algorithm for the measurement of traffic noise, whole time level distribution can be found. Computer model is able to consider the traffic in more detail in real sense having more dependent parameters. From the measured data from different sides of Sylhet, it is found that noise of density is not significantly affected by residential density. The noise level on the main road near residential area, hospital area and educational area are above the recommended level (65dBA). It was found that the predictive equations are in 60-70% correlated with the measured noise level. The mathematical relation developed in the study will help degree of discomfort while a road network in colony is being planned.

REFERENCES