快樂方式

Introduction 

The objective of this measurement is to investigate the traffic noise reduction performance of noise barrier, observe the noise level of position behind the noise barrier (lower than 3 meters) and the position above of noise barrier (higher than 3 meters), and then conduct a comparison of the data record in this two position. At the same time, number of vehicles which pass the front of measuring location should be count. This measuring method can show how high level of noise barrier can adsorb and obstruct from road. 

In this measurement, a location which is adjacent to A Kung Kok Road and have installed noise barrier between measuring location and A Kung Kok Road was chosen. This is a suitable location to conduct measurement due to the high traffic volume of A Kung Kok Road. 

Methodology 

Before measurement, an accessible location with noise barrier adjacent to a road is necessary to find, as mention above, a location which have installed noise barrier adjacent to A Kung Kok Road and next to A Kung Kok Village , the sensitive receiver of traffic noise from A Kung Kok Road has been found. On the other hand, equipment are also need to prepare: Precision sound level meter, calibrator, tripod, extension cable, extension rod and tape measure. After arrive to measuring location ,before measurement, sound level meter should be calibrate before measurement to ensure the sensitive of sound level meter. Then, place sound level meter with a tripod and windscreen at the location that is shielded by the noise barrier. After that, conduct a 30 minutes measurement at the location with barrier shield (lower than 3 meters) and without barrier shield (higher than 3 meters), Leq should be record per every 3 minutes. During measurement, traffic volume should also be measure, the method of measure traffic volume is to count the vehicle pass the front of measuring location and then mark the number of number of vehicles. After 30 minutes measurement, other parameter: L10, L90 and Lmax with 30 minutes interval should be record. Second time sound level calibration should be conduct at the end of measurement 

Result 

1. Noise level (with shielding by noise barrier): 

During measurement, noise level with parameter Leq, L10 and L90 with barrier has been measured, The result of noise level with noise level are as follow:  

30 minute Leq was 61.6dB, L10 equal to 64dB and L90 equal to 57dB. To view the Leq trend in 30 minutes measure interval, it is comparatively ups and downs, there has a downward trend from minute 0 61,3dB decrease to 57.2dB ate minute 6, and then a slightly upward trend from 57.2dB increase to 58.6dB are exceed at the interval between minute 6 to minute 9. A downward trend from minute 9 58.6dB to minute 12 55.3dB. After minute 12, a upward trend from 55.3dB to 63.7dB continue for six minutes from minute 12 to minute 18, another upward trend was present from minute 21 to minute minute 27 with Leq 59.8dB to 64.2dB. At the end of measurement, a downward trend are present.  

For the aspect of vehicle type, 4 type of vehicle: bus, truck, private car and motorcycle were observed, total 211 vehicles were marked. Among this 4 types of vehicle, the most frequent are private car with 107 vehicles, following private car, bus are the second frequent vehicle type with 68 vehicles.  

Calibration before measurement : 93.9dB 

Time (min)	Leq	L10	L90	Leq (30 min)	Lmax (30 min)
0	61.3	64	57
3	60.6
6	57.2
9	58.6
12	55.3
15	60.1
18	63.7
21	59.8
24	63.1
27	64.2
30	59.7			61.6	75.5

alibration after measurement: 

 

Line chart of 3 minute Leq log with barrier 

 

Number of vehicles: 

Vehicle type	Number of vehicle
Bus	68
Truck	30
Private car	107
Motorcycle	6
Total	211

1. Noise Level (without shielding by noise barrier) 

Calibration before measurement: 93.9d 

During measurement, noise level with parameter Leq, L10 and L90 without barrier has been measured, The result of noise level with noise level are as follow:  

30 minute Leq was 60.6dB, L10 equal to 63dB and L90 equal to 57.2dB. To view the Leq trend in 30 minutes measure interval, it is comparatively ups and downs, overall, there had three upward trend and three downward trend. A upward trend from minute 0 58.8dB increase to 63.2dB ate minute 6, and then a slightly downward trend from 63.2dB decrease to 57.9dB are exceed at the interval between minute 3 to minute 9. A upward trend from minute 9 57.9dB to minute 15 66.2dB. After minute 15, a downward trend from 66.2dB to 59.8dB continue for six minutes from minute 15 to minute 21, another upward trend was present from minute 21 to minute minute 27 with Leq 59.8dB to 61.4dB. At the end of measurement, a downward trend are present.  

For the aspect of vehicle type, 4 type of vehicle: bus, truck, private car and motorcycle were observed, total 190 vehicles were marked. Among this 4 types of vehicle, the most frequent are bus with 80 vehicles, following bus, private car are the second frequent vehicle type with 66 vehicles.  

Time (min)	Leq	L10	L90	Leq (30 min)	Lmax (30 min)
0	58.8	63	57.2
3	63.2
6	60.5
9	57.9
12	61.4
15	66.2
18	61.7
21	59.8
24	64.4
27	61.4
30	59.1			60.6	70

Calibration after measurement: 93.9dB 

 

Line chart of 3 minute Leq log without barrier 

 

Number of vehicles: 

Vehicle type	Number of vehicle
Bus	80
Truck	38
Private car	66
Motorcycle	6
Total	190

Discussion 

To compare the sound pressure level of different minutes in measuring interval, there are significant discrepancy with the data. For the aspect of with barrier, the sound pressure level at the beginning (3 minute), middle (15 minute)and later period (24 minute) of measuring interval, the sound pressure level were high compare to other minutes during measuring period, at the minute that mention above, those sound pressure level were excessed 60 dB, the lowest sound pressure level at measuring interval with barrier were around 57-59 dB.  It is possible that traffic volume was effect the result directly, when the traffic volume is high, sound volume will relative high, sound pressure level will high, when the traffic volume is low, sound volume will relative low, sound pressure level will low.  

For the aspect of without barrier, the sound pressure level was higher than without barrier, the highest sound pressure level was 66.2 dB while the lowest sound pressure level was 57.9 dB at the measuring interval. 

To compare the result with measure with barrier and without barrier, it can shows that the performance of reduce sound of barrier was not very good, the barrier can reduce little sound from road, because the sound pressure level of measure with barrier just slightly decrease, and the sound pressure level measurement with barrier were higher than measurement without barrier at few minutes during measure interval. For example at the beginning (3 minute), middle (15 minute) and later period (24 minute), the sound pressure level with barrier was 60.6dB, 60.1dB and 63.1dB respectively, while without barrier was 63.2 dB, 66.2dB and 64.4dB, it shows that the sound pressure level just slightly dropped after reduce by barrier.  

According to the field measurement, the location of sound meter may affect the accuracy of the sound level due to sound pressure level will decrease if the sound meter is far from sound source,  sound energy will be adsorb by air molecule and cause sound gradual weakening, longer distance between sound source, more sound will be weakening, so this situation can not show the real situation of noise impact from traffic on road. The best distance between sound meter and sound source or barrier is around 1-2m,  

On the other hand, the human activities conduct behind the sound meter will also affect the accuracy of the sound level, because human activities conduct behind sound meter may produce other noise apart from noise from vehicles on road. Sound meter will also measure noise produce from human activities, the sound measure result will include noise produce from human activities and traffic noise on road at the same time. The aim of this measurement is to measure noise from vehicles, so it can not present the real result when human activities produce noise.