An investigation on time-interval optimisation of traffic noise measurement

Noise is one of the most important sources of pollution in metropolitan areas, it causes discomfort for urban residents and hampers the efficiency of the work force. Currently, there is an urgent need to conduct basic studies on this issue in order to attain a mathematical model for prediction of traffic noise levels in the major cities of Iran. This article is the result of research conducted in the city of Hamadan in 2005 with the ultimate objective of setting up a traffic noise model based on the traffic conditions of Iranian cities. For this study, main access roads of Hamadan city were divided in 64 segments and after careful considerations, 94 measuring stations were assigned to them. For the optimisation of noise measurement intervals in each station and the determination of background noise impact on the main traffic noise, 30 stations with the specifications of the target stations were randomly selected at the pilot stage. In all the pilot stations, the background sound pressure level (SPLb), L-eq, SPLmax, L-10 were measured simultaneously in 10, 30 and 60 minute intervals (in random non-holiday days at random hours). The measurements were made 3 meters away from the road side. Pilot results indicated that the mean equivalent sound pressure levels at the measuring stations in 10, 30 and 60 minute intervals were 70.76 +/- 2.11 dBA, 30 minutes 70.88 +/- 2.19 dBA, and 60 minutes 70.93 +/- 2.13dBA respectively. The mean background sound pressure level at the stations was 60.77 +/- 5.04 dBA. The results of the traffic noise measurements at the research stations through the comparison of mean values (Variance Analysis) indicated that there is no meaningful deviation between the L, in the above-mentioned time intervals (10, 30 and 60 minutes) in the hourly measurements (P= 0.998). In the pilot phase, it was determined that the background noise level did not impose a considerable impact on the main traffic noise and it was possible to make 10-minute interval measurements to forecast the 30-minute and 60-minute interval equivalent levels. Therefore in the main phase of study with the utilisation of the 10-minute interval results collected from each of the 94 stations, a total of 282 measurements including 2 daily-hour and one nightly-hour measurements were conducted. The final results revealed that the average Leq in all stations was 69.04 +/- 4.25 dBA, the average speed of vehicles was 44.57 +/- 11.46 km/hr and average ,e traffic load was 1231.9 +/- 910.2 V/hr. Moreover, the results indicated that the L-eq in the studied roads were exceeding the allowable levels of urban noise pollution and there was a meaningful deviation between equivalent levels during a 24-hour period, traffic load and various vehicle speeds (P = 0.003).