A case study of acoustic efficiency of existing noise barrier in reducing road traffic noise in school area

The study investigates the effectiveness of existing noise wall barrier installed in a school for shielding noise from heavy traffic. The objectives of this study are to investigate the effect of this barrier on the characteristic of traffic noise spectra, and evaluate its efficiency on broadband noise insertion loss and low frequency noise attenuation. The barrier is of absorptive type with slightly aging condition where small holes and cracks in some places are spotted in both surfaces of wall. The barrier is made of panels of fibre cement mortar infill with absorbent materials with the height is 4m x 0.25m thickness x 132 m length with the distance of the barrier to the highway as main noise source is 17 m. Investigation of the efficiency of barrier started with the determining of noise frequency spectra near the barrier at 0.5m in front of barrier, and 0.5 m and 6m behind the barrier, all at five points along the barrier length. The efficiency of barrier was determined by its insertion loss of broadband noise and attenuation of low frequency in the range 20 to 200 Hz. The results showed that barrier changed the characteristic of traffic noise spectrum. It was found that barrier efficiently achieved insertion loss of 5 dBA or above if the receiver was at distance more than 3.5m behind the wall. At 6m meter behind wall, although the barrier was considered effective but it was failed in reducing the sound pressure level below the World Health Organisation (WHO) permissible limit for school area and attenuating the low frequency noise sufficiently. These results highlighted that the barrier unable to combat the noise disturbance in school playing field area.