Traffic Noise Modelling Considering Various Traffic Compositions At Roundabouts

Abstract

like Cars, S.U.V., Heavy Vehicles, Three wheelers and Two wheelers. Many western countries have developed different prediction models based on Leq, L10 and other characteristics. The heterogeneous feature of traffic noise at roundabouts, together with the characteristics of environmental noise, with their spatial, temporal an spectral variability, makes the matter of modeling and prediction a complex and non linear problem, therefore a need is being felt to develop a traffic noise prediction model for roundabouts considering various class of vehicles suitable for Indian conditions, acceleration, deceleration and distance from road. The present work represents a traffic prediction model taking Fountain Chowk, Thikkari Chowk, and Y.P.S. Chowk, Patiala as three roundabouts for high, medium and low traffic volume conditions respectively for representative/demonstrative site. All the measurement for noise level, traffic volume, acceleration, deceleration and distance were measured at selected points around the roundabouts at different time intervals on number of days in a random/staggered manner in order to account for statistical temporal variations in traffic flow conditions. The noise parameters recorded are Traffic volume for each vehicle class, average acceleration and deceleration for vehicles, distance of point of measurement from road median/ roundabout and the noise descriptors recorded are Equivalent Noise Level(Leq), Percentile Noise levels (L10 ,L50 and L90).Effects of noise parameters on noise descriptors were also studied. To get the overall noise climate around the roundabouts, Leq (Single value representing the noise iv level during measurement time) and three percentile levels (L90 for judging and assessing the pervasive noise climate; L50 corresponding to average noise climate and L10 for maximum level of noise exposure) were studied. A multiple regression approach has been applied for traffic noise modeling in the present study. The measured parameters were divided into four classes i.e. dependent parameters or response parameters (Leq, L10, L50 and L90) and input parameters as (Vehicles volume per hour for each class, average acceleration and deceleration, distance of measurement point from road). After carrying out the analysis the multiple R or correlation coefficient were found to be 0.84 for Leq, 0.85 for L10, 0.85 for L50, and 0.88 for L90 stating that there is good correlation between the actual and the model predicted values. Also the respective R2 values were 0.70 for Leq, 0.79 for L10, 0.78 for L50, 0.84 for L90. The percentage error was found to be varying between ±3% for all the sound descriptors Correlation test was carried out to find out the most affecting factor for a particular sound descriptor and a rank is assigned to all the factors. Negative correlation was found for road width ‘l’ stating an attenuating effect between Noise level and ‘l’. A t-test was also carried out to check for any significant difference between the measured sound level and the predicted sound level mean values. The test stated no significant difference between the measured and predicted sound levels. Frequency analysis for 1/1 Octave band was monitored for certain days to get a feel of the dominant frequencies range. The results stated that 500 Hz., 1kHz. and 2kHz frequency components dominate in the spectrum thus causing more annoyance (1 kHz to 4 kHz). This information is quite useful and necessary for barrier design. The barrier design analysis should consider the material requirement that have more absorption coefficient to abate the peak noise level at these frequencies. On comparison of three roundabouts weekly average traffic noise it is found that the maximum noise was found to be at Thikkari Chowk Roundabout with Leq of 78.8 dB (A) , then Fountain Chowk with Leq of 76.7 dB (A) and least for Y.P.S. Chowk Roundabout with Leq of 73.3 dB (A). These are above the permissible values therefore mitigating measures are necessary to improve the noise climate.