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Characteristics of road traffic noise in Hanoi and Ho Chi Minh City, Vietnam
Applied Acoustics 71 (2010) 479–485
Contents lists available at ScienceDirect
Applied Acoustics journal homepage: www.elsevier.com/locate/apacoust
Technical Note
Characteristics of road traffic noise in Hanoi and Ho Chi Minh City, Vietnam Hai Yen Thi Phan a,*, Takashi Yano a,1, Tetsumi Sato b,2, Tsuyoshi Nishimura c,3 a
Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, 860-8555 Kumamoto, Japan Faculty of Engineering, Hokkai Gakuen University, Minami 26-Jo, Chuo-ku, 064-0926 Sapporo, Japan c Graduate School of Engineering, Sojo University, 4-22-1 Ikeda, 860-0082 Kumamoto, Japan b
a r t i c l e
i n f o
Article history: Received 7 August 2009 Received in revised form 6 November 2009 Accepted 12 November 2009 Available online 5 December 2009 Keywords: Characteristics of traffic noise Noise exposure Motorbikes Horn sounds
a b s t r a c t Noise pollution due to road traffic is a major global concern because of its negative impact on the quality of life in communities everywhere. In Vietnam, traffic noise has become an increasingly noticeable and serious problem in large cities like Hanoi and Ho Chi Minh City. To gain more insight into the characteristics of this noise, intensive noise measurements were conducted in Hanoi and Ho Chi Minh City in September 2005 and September 2007, respectively. A comprehensive dataset of noise was obtained that included 24-h noise measurements as well as short-term noise recordings. The volume of traffic was also quantified by reproducing video camera recordings. Noise datasets from both cities were then compared with a dataset of Japanese traffic noise obtained in Kumamoto. The results showed that the traffic noise in Hanoi and Ho Chi Minh City was characterized by relatively high noise exposure levels due to the large number of motorbikes and frequent horn sounds. The sound of horns contributed a definite impact of 0– 4 dB on noise exposure in Hanoi and Ho Chi Minh City, where noise levels decreased with the absence of horn sounds. Our results also showed differences in the characteristic traffic noise of Vietnam and Japan. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction Noise pollution in urban areas has been globally recognized as a major detriment to the quality of life. The adverse effects of noise include various impacts on people’s physical well-being [1] and the disturbance of daily activities [2]. Actions to control such effects have been an immediate concern for communities in countries of the developed world, as evidenced by a large body of regulations and noise policies [3–7]. Such action remains limited, however, in the developing countries, especially in Asia. In Southeast Asia, Vietnam is among the developing countries whose urban environment has undergone significant changes due to industrialization, urbanization, and the relentless increase in the number of motor vehicles over the last 5 years. These changes have probably led to an increase in noise levels that have negative effects on the citizens. Despite this, Vietnam has not yet developed a practical policy to cope with the situation. As two of the largest and most important cities in Vietnam, Hanoi and Ho Chi Minh City present strong subjects for case studies of noise pollution due to road traffic in urban areas.
* Corresponding author. Tel./fax: +81 80 3220 0460. E-mail addresses: [email protected] (H.Y.T. Phan), [email protected] (T. Yano), [email protected] (T. Sato), [email protected], [email protected] (T. Nishimura). 1 Tel.: +81 96 342 3560. 2 Tel.: +81 11 841 1161. 3 Tel.: +81 96 326 3605. 0003-682X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.apacoust.2009.11.008
Hanoi is the capital city that in 2007 had an urban population of approximately 6.23 million. Ho Chi Minh City’s population currently exceeds 7 million, not counting 2 million who live there as temporary residents or commuters. In these big cities, apart from buses, which provide the only public transportation, the dominant vehicle is the motorbike due to its cost, flexibility, and adaptability to road conditions. According to statistics from the World Bank, the number of motorbikes in Vietnam has reached 20 million—one of the highest per capita levels in the world—and motorbikes account for nearly 96% of all local transportation. In Hanoi and Ho Chi Minh City, motorbikes serve up to 85% of the population’s travel needs, which results in chaotic traffic flow and excessive horn blowing throughout the day. Fig. 1 shows an example of traffic conditions in Vietnam. One of the primary goals of the present study, therefore, was to evaluate environmental noise pollution in urban sections of Hanoi and Ho Chi Minh City. This study is intended as the first step toward determining the characteristics of traffic noise in these Vietnamese cities. In addition, noise measurements were also performed in Kumamoto, Japan, in order to obtain a noise dataset from a city of a developed country in Asia. The main goal is to compare the traffic noise situation between Vietnam and Japan. 2. Methods 2.1. Investigated sites Seven sites were selected in Hanoi and eight in Ho Chi Minh City, all of which are typical urban neighborhoods with a
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Fig. 1. Road traffic conditions in Vietnam.
Fig. 2. Map of noise measuring sites in Hanoi.
condensed mixture of commercial and residential activities and public utilities. In Hanoi, Sites 2, 6 and 7 are among the busiest roads. Site 2 is a small one-lane street that mainly connects the boundary points of the city without crossing the city’s central zone. One of the biggest universities (Hanoi University of Medicine) is located here. The street of Site 6 mainly connects the boundary points of the city’s central zone and is therefore busy most of the time. The streets of Sites 4 and 7 link the city center with the western and northern highways, respectively. They therefore endure remarkably heavy traffic, which includes motorbikes and cars during the day and heavy vehicles at night. The situation is almost the same for Sites 4 and 7 in Ho Chi Minh City, whose streets link the central zone of the city with the highway that leads to the western suburbs. Among all the sites, Site 7 is one of the most densely populated areas. The street of Site 6 is the narrowest, compared to those in other sites, but its volume of traf-
fic is remarkably high because it offers a shortcut from the city to the western highway. In Kumamoto, two sites were selected. Site 1 is a narrow twolane street where a university (Kumamoto University) is located. Site 2 is a bigger four-lane street connecting the boundary points of the city without crossing the city’s central zone. 2.2. Noise measurement Our acoustic surveys were conducted in September 2005 and September 2007 in Hanoi and Ho Chi Minh City, respectively. The measurement sites in Hanoi and Ho Chi Minh City are displayed in Figs. 2 and 3, respectively. A 24-h noise measurement was conducted at a reference point 1.2 m above ground, and 1–12 m away from the road shoulder by means of sound level meters (Rion NL06 and NL-22). A-weighted sound pressure levels were measured
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Fig. 3. Map of noise measuring sites in Ho Chi Minh City.
Table 1 Traffic volume in Hanoi, Ho Chi Minh City, and Kumamoto.
Hanoi Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7
Number of lanes
QM
QC
QH
% of QM
% of QC
% of QH
QM + QC + QH
4 1 4 6 4 4 6
87,184 137,785 73,981 77,597 89,814 166,610 182,032
14,968 9502 5399 5699 4063 10,829 16,559
2668 1496 543 531 1360 5435 1403
83 93 93 93 94 91 91
14 6 7 7 4 6 8
3 1 1 1 1 3 1
104,819 148,783 79,922 83,827 95,237 182,874 199,994
116,429
9574
1919
91
7
2
127,922
33,444 67,359 156,060 156,096 131,196 73,584 239,031 201,924
198 590 7584 6816 5472 2208 13,773 11,064
12 407 936 2580 3468 792 4974 5496
99 99 95 94 94 96 93 92
1 1 5 4 4 3 5 5
0 1 1 2 2 1 2 3
33,654 68,356 164,580 165,492 140,136 76,584 257,778 218,484
132,337
5963
2333
94
4
2
140,633
3030 3486
19,236 44,628
1020 2700
13 7
83 88
4 5
23,286 50,814
Average
Ho Chi Minh City Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7 Site 8
1 1 2 4 4 1 2 4
Average
Kumamoto Site 1 Site 2
2 4
every second for 24 h. Additional noise measurements at 10-min intervals, together with noise recordings, were conducted at seven sites in Hanoi and eight sites in Ho Chi Minh City in order to obtain data for frequency analysis. During the 24-h noise measurement, traffic volume by vehicle type was also monitored by video camera. The sampling time interval was 10 min in each hour. Traffic quantification was performed later after reproduction of the video recording. Traffic flows were grouped into three vehicle categories: QM = motorbikes, QC = cars/light trucks, and QH = heavy vehicles.
Noise measurements in Kumamoto were conducted at the two selected sites in June 2007 applying the similar method that was used in both Vietnamese cities. 3. Results and analysis 3.1. Traffic volume characteristics Table 1 presents the traffic data collected from each site in Hanoi, Ho Chi Minh City, and Kumamoto. Since QM in Site 2 in
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Fig. 7. Motorbike volume data from Ho Chi Minh City spanning 24 h. Site 2; Site 3; Site 4; Site 5; Site 6; Site 7;
Fig. 4. Hourly traffic volume data from Site 2 in Hanoi.
Site 1; Site 8.
Fig. 8. Sound level fluctuations at 17:00. - - - Kumamoto data (Site 2); — Ho Chi Minh data (Site 5). Fig. 5. Hourly traffic volume data from Site 5 in Ho Chi Minh City.
Fig. 9. Hourly noise levels of Site 2 in Hanoi.
Fig. 6. Motorbike volume data from Hanoi spanning 24 h. Site 3; Site 4; Site 5; Site 6; Site 7.
Site 1;
Site 2;
Hanoi and Site 5 in Ho Chi Minh City are relatively equivalent to the average number of motorbikes in both cities, the overall results from these two sites are considered as representative illustrations throughout Section 3. The daily average number of vehicles from all sites is estimated at about 128,000 vehicles in Hanoi and 140,000 in Ho Chi Minh City. While QM plays the most significant role in the traffic of both Vietnamese cities, QC is found to be more common in Kumamoto, accounting for >80% of the city’s total traffic. On average, 91% of the total traffic in Hanoi is accounted for by
motorbikes, as is 94% of the total traffic in Ho Chi Minh City. Examples of the collected traffic flow data for Site 2 in Hanoi and Site 5 in Ho Chi Minh City are reported in Figs. 4 and 5, respectively, where time variations in the hourly traffic volume are plotted for each vehicular group. In both figures, QM is reflected in the left axis and QC and QH in the right axis. Both cities exhibit an almost similar trend in which there is more QM and QC during the day, and less QM and QH at night or in the early morning hours. In terms of heavy traffic, in Ho Chi Minh City, an increase in QH can be observed during the noon-time hours, which remains the same for every site. In Hanoi, QH is much less compared to QM and QC at Site 5. Nevertheless, at other sites in Hanoi, QH increases slightly during the night time.
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Fig. 12. Relative cumulative frequency of noise levels at Site 2 in Hanoi and Site 5 in Ho Chi Minh City, compared with Site 2 in Kumamoto, Japan.
Fig. 10. Hourly noise levels of Site 5 in Ho Chi Minh City.
Fig. 11. Hourly noise levels of Site 2 in Kumamoto. Fig. 13. 1/3-Octave-band frequency analysis of Site 2 in Hanoi and Site 5 in Ho Chi Minh City, compared with Site 2 in Kumamoto, Japan.
Table 2 Noise levels in Hanoi, Ho Chi Minh City, and Kumamoto. Noise metrics (dB)
LAeq,day
LAeq,night
LAeq24h
L1
L5
L10
L50
L90
L95
L99
Hanoi Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7
76 72 76 74 69 71 77
72 66 71 69 65 65 76
75 71 75 73 68 70 77
84 81 85 82 75 79 85
79 76 79 76 72 74 81
77 73 77 75 70 72 79
73 68 72 70 67 67 75
61 54 59 60 54 56 68
55 49 53 55 49 51 64
48 46 45 49 43 47 58
Ho Chi Minh City Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7 Site 8
74 77 78 72 76 78 76 78
69 72 74 68 71 71 73 76
72 76 77 71 74 76 75 77
81 85 85 79 82 86 83 86
77 80 81 75 79 80 79 81
75 78 80 74 77 79 78 80
70 73 76 70 73 74 74 76
57 61 66 62 64 65 67 71
52 56 61 58 61 64 64 69
47 50 53 52 55 60 59 64
Kumamoto Site 1 Site 2
70 70
66 67
68 69
76 77
73 74
71 73
65 66
51 53
45 49
37 42
Figs. 6 and 7 present data regarding the volume of motorbikes in Hanoi and Ho Chi Minh City, respectively. In both cities, the maximum amount of QM was observed in the morning and evening rush hours, and the least density of QM was observed from 01:00 a.m. to 06:00 a.m. The site-by-site variation in QM in Ho Chi Minh City is greater than in Hanoi due to the fact that Sites 1, 2, and 6 in Ho Chi Minh City were smaller one-lane streets compared to the rest of the sites.
3.2. Noise exposure Since the traffic noise patterns in Hanoi and Ho Chi Minh City are nearly identical, a representative noise pattern from Ho Chi Minh City was taken to compare with a noise pattern from Kumamoto. Fig. 8 presents the level of random sound fluctuation obtained in a 300-s timeframe at Site 5 in Ho Chi Minh City, and at Site 2 in Kumamoto. The noise levels in Ho Chi Minh City fluctuate
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Table 3 Results of noise levels with and without horn sounds for Hanoi and Ho Chi Minh City. Noise metrics (dB)
Site 1
Site 2
Site 3
Site 4
Site 5
Site 6
Site 7
Hanoi LAeq,10 min LAeq without horn sound LAeq difference LAeq horn sound % of time occupied by horn sound
68 67 1 75 8
69 65 4 77 12
67 66 1 63 5
68 67 1 64 9
66 65 1 59 4
66 63 3 63 6
68 66 2 63 9
– – – – –
Ho Chi Minh LAeq,10 min LAeq without horn sound LAeq difference LAeq horn sound % of time occupied by horn sound
73 73 0 78 4
74 74 0 81 2
67 66 1 75 5
66 65 1 72 4
67 67 0 74 4
71 70 1 75 9
69 67 2 75 12
68 67 1 74 5
by approximately 10 dB, with frequent sharp peaks due to audible horn sounds, which indicates that the traffic noise in this city has an impulsive, percussive character. This is different from the sound levels in Kumamoto, which vary by as much as 20 dB, but in which the traffic noise level increases and decreases in a predictably periodic signal pattern. Examples of the measured acoustic data are reported in Figs. 9– 11, where the time variation in the A-weighted sound level Leq and in the percentile sound levels L1, L10, L50, L90 and L99, are plotted for Sites 2, 5, and 2 in Hanoi, Ho Chi Minh City, and Kumamoto, respectively. In Table 2, the average values of the noise levels for all sites investigated in the three cities are also listed. In the overall monitoring sites in Hanoi and Ho Chi Minh City, the daily average noise levels LAeq,day were >69 dB. In general, it was clearly observed that the noise levels in Hanoi and Ho Chi Minh City were higher than those in Kumamoto. In Figs. 9 and 10, the time variation in noise levels is almost the same for Hanoi and Ho Chi Minh City. In these cities, the percentile level L1 is obviously quite high, as it was determined by the emission of horn sounds. In Kumamoto, the L1 level did not vary much over 24 h, and the difference between L1 and L10 was smaller than the corresponding values of the difference in both Hanoi and Ho Chi Minh City. Percentile sound levels L90 and L99 can be considered as background noise levels. A decrease in background noise levels could be detected at night in both Hanoi and Ho Chi Minh City, although the decrease was more pronounced in Hanoi. In Kumamoto, the background noise level was found to be quite low. An example of the relative cumulative frequency of noise levels at Sites 2 and 5 in Hanoi and Ho Chi Minh City, respectively, is shown in Fig. 12, in comparison with traffic noise levels at Site 2 in Kumamoto. It can be seen that the traffic noise in Kumamoto is approximately 5-dB lower than that in Hanoi, but about 10 dB lower than that in Ho Chi Minh City. It is also worth noting that due to horn sounds, the slope of the curves for Hanoi and Ho Chi Minh City is steeper than that for Kumamoto.
3.3. Frequency analysis Fig. 13 compares the results of 1/3-octave-band frequency analysis in Hanoi and Ho Chi Minh City with corresponding results obtained for Kumamoto. Visible peaks can be observed at the lowfrequency range from 80 to 160 Hz in all three cities. The peaks at 125 Hz may be due to noise emitted by motorbike engines in Hanoi and Ho Chi Minh City, and the peak at 80 Hz in Kumamoto may be attributed to car engines. At 3.15 kHz, another two peaks could be detected in Hanoi and Ho Chi Minh City, which were probably caused by horn sounds.
Site 8
3.4. Effect of horn sound on noise exposure From the above findings, it is notable that traffic noise in Hanoi and Ho Chi Minh City has an impulsive, percussive character that is mainly due to frequent horn sounds. At a maximum, horn sounds occupied 12% of the total measurement time in both cities (see Table 3). In order to examine the possible effect of horn sound on noise exposure, the horn sounds were removed from the obtained LAeq,10 min. Table 3 presents results showing that traffic noise in Hanoi decreases by at least 1 dB after horn sounds are removed, while traffic noise in Ho Chi Minh City decreases by 0.7 dB on average. The effect of horn sounds was found to be slightly more pronounced in Hanoi than in Ho Chi Minh City. Although horn sounds contribute a relatively small amount to the total noise exposure, their psychological impact may be greater because of the startling effects of such noise. In a paper investigating the impact of horn sounds on two groups of Vietnamese and Japanese subjects, Phan et al. [8] found that horn sounds had a severe effect on the Japanese subjects and created great annoyance within the group. With regard to the role of impulsive sounds in international standards, the newly revised version of ISO R 1996 [9,10] recommends a 5-dB penalty for impulsive noise, while another study suggests penalties of 10 dB [11]. Thus, in order to predict the community response to traffic noise in cities such as Hanoi and Ho Chi Minh City, it is necessary to investigate the relationship between horn sounds and annoyance. 4. Conclusion Our acoustic surveys in Hanoi and Ho Chi Minh City revealed that in cities of a developing country, environmental noise levels due to traffic are notably higher than those in a developed country such as Japan. Moreover, while cars are the common form of transportation in developed countries, motorbikes are by far the dominant vehicle in the traffic in Vietnam. In general, high noise levels are the result of frequent horn sounds, especially in Hanoi. From our overall site monitoring, the daily average noise levels LAeq,day were >69 dB. The current study is intended as a first step toward determining the characteristics of traffic noise in two major Vietnamese cities. In future studies, we aim to provide fundamental data on the physical characteristics of current noise pollution and to evaluate the population’s response to this increasingly detrimental phenomenon. Acknowledgements This study has received the joint financial support of the Core University Program that includes the Japan Society for the Promo-
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tion of Science (JSPS), the National Center for Science and Technology (NCST), Grant-in-Aid for Scientific Research (Project No. 17560533), and a Kajima Foundation Research Grant (2006). The authors highly appreciate the insightful academic advice on the conducting of noise measurement given by Professors P.N. Dang, L.V. Nai, and P.D. Nguyen of the Hanoi University of Civil Engineering, and by Ms. N.T. Bich Ngoc of the Ho Chi Minh University of Architecture. The authors would also like to thank the students of the Hanoi University of Civil Engineering and Ho Chi Minh University of Architecture for their vital assistance in the maintenance of equipment during measurement proceedings. References [1] Davies H, Van Kamp I. Environmental noise and cardiovascular disease: five year review and future directions. In: Proceedings of ICBEN 2008; 2008. [2] Finegold LS, Harris CS, von Gierke HE. Community annoyance and sleep disturbance: updated criteria for assessing the impacts of general transportation noise on people. Noise Control Eng J 1994;42(1).
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[3] Miedema HME. Annoyance caused by environmental noise: elements for evidence-based noise policies. J Soc Issues 2007;63(1):41–57. [4] Noise abatement and control: department policy, implementation responsibilities, and standards. Washington, DC, US Department of Housing and Urban Development Circular 1390.2 (August 1971). [5] Berglund B, Lindvall T. Community noise—document prepared for the World Health Organization. Arc Center Sens Res 1995;2:86–103. [6] Environmental Protection Agency 1978 EPA Document, November, 550/9-79100, USA Protective noise levels. [7] Commission of the European Communities, Directive of the European Parliament and of the Council relating to the Assessment and Management of Environmental Noise, COM (2000) 468 final. [8] Phan HAT, Yano T, Phan HYT, Sato T, Hashimoto Y. Annoyance caused by road traffic with and without horn sounds. Acoust Sci Tech 2009;30(5):327–37. [9] ISO Acoustics 1996-1:2003. Description, measurement and assessment of environmental noise – part 1: basic quantities and assessment procedures. Geneva: ISO; 2003. [10] ISO Acoustics 1996-2:2007. Description, measurement and assessment of environmental noise – part 2: determination of environmental noise levels. Geneva: ISO; 2007. [11] Groeneveld Y, de Jong RG. CEC joint project on impulse noise: overall results of the field survey. In: Proceedings of internoise 1985; 1985 p. 905–8.
Contents lists available at ScienceDirect
Applied Acoustics journal homepage: www.elsevier.com/locate/apacoust
Technical Note
Characteristics of road traffic noise in Hanoi and Ho Chi Minh City, Vietnam Hai Yen Thi Phan a,*, Takashi Yano a,1, Tetsumi Sato b,2, Tsuyoshi Nishimura c,3 a
Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, 860-8555 Kumamoto, Japan Faculty of Engineering, Hokkai Gakuen University, Minami 26-Jo, Chuo-ku, 064-0926 Sapporo, Japan c Graduate School of Engineering, Sojo University, 4-22-1 Ikeda, 860-0082 Kumamoto, Japan b
a r t i c l e
i n f o
Article history: Received 7 August 2009 Received in revised form 6 November 2009 Accepted 12 November 2009 Available online 5 December 2009 Keywords: Characteristics of traffic noise Noise exposure Motorbikes Horn sounds
a b s t r a c t Noise pollution due to road traffic is a major global concern because of its negative impact on the quality of life in communities everywhere. In Vietnam, traffic noise has become an increasingly noticeable and serious problem in large cities like Hanoi and Ho Chi Minh City. To gain more insight into the characteristics of this noise, intensive noise measurements were conducted in Hanoi and Ho Chi Minh City in September 2005 and September 2007, respectively. A comprehensive dataset of noise was obtained that included 24-h noise measurements as well as short-term noise recordings. The volume of traffic was also quantified by reproducing video camera recordings. Noise datasets from both cities were then compared with a dataset of Japanese traffic noise obtained in Kumamoto. The results showed that the traffic noise in Hanoi and Ho Chi Minh City was characterized by relatively high noise exposure levels due to the large number of motorbikes and frequent horn sounds. The sound of horns contributed a definite impact of 0– 4 dB on noise exposure in Hanoi and Ho Chi Minh City, where noise levels decreased with the absence of horn sounds. Our results also showed differences in the characteristic traffic noise of Vietnam and Japan. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction Noise pollution in urban areas has been globally recognized as a major detriment to the quality of life. The adverse effects of noise include various impacts on people’s physical well-being [1] and the disturbance of daily activities [2]. Actions to control such effects have been an immediate concern for communities in countries of the developed world, as evidenced by a large body of regulations and noise policies [3–7]. Such action remains limited, however, in the developing countries, especially in Asia. In Southeast Asia, Vietnam is among the developing countries whose urban environment has undergone significant changes due to industrialization, urbanization, and the relentless increase in the number of motor vehicles over the last 5 years. These changes have probably led to an increase in noise levels that have negative effects on the citizens. Despite this, Vietnam has not yet developed a practical policy to cope with the situation. As two of the largest and most important cities in Vietnam, Hanoi and Ho Chi Minh City present strong subjects for case studies of noise pollution due to road traffic in urban areas.
* Corresponding author. Tel./fax: +81 80 3220 0460. E-mail addresses: [email protected] (H.Y.T. Phan), [email protected] (T. Yano), [email protected] (T. Sato), [email protected], [email protected] (T. Nishimura). 1 Tel.: +81 96 342 3560. 2 Tel.: +81 11 841 1161. 3 Tel.: +81 96 326 3605. 0003-682X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.apacoust.2009.11.008
Hanoi is the capital city that in 2007 had an urban population of approximately 6.23 million. Ho Chi Minh City’s population currently exceeds 7 million, not counting 2 million who live there as temporary residents or commuters. In these big cities, apart from buses, which provide the only public transportation, the dominant vehicle is the motorbike due to its cost, flexibility, and adaptability to road conditions. According to statistics from the World Bank, the number of motorbikes in Vietnam has reached 20 million—one of the highest per capita levels in the world—and motorbikes account for nearly 96% of all local transportation. In Hanoi and Ho Chi Minh City, motorbikes serve up to 85% of the population’s travel needs, which results in chaotic traffic flow and excessive horn blowing throughout the day. Fig. 1 shows an example of traffic conditions in Vietnam. One of the primary goals of the present study, therefore, was to evaluate environmental noise pollution in urban sections of Hanoi and Ho Chi Minh City. This study is intended as the first step toward determining the characteristics of traffic noise in these Vietnamese cities. In addition, noise measurements were also performed in Kumamoto, Japan, in order to obtain a noise dataset from a city of a developed country in Asia. The main goal is to compare the traffic noise situation between Vietnam and Japan. 2. Methods 2.1. Investigated sites Seven sites were selected in Hanoi and eight in Ho Chi Minh City, all of which are typical urban neighborhoods with a
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Fig. 1. Road traffic conditions in Vietnam.
Fig. 2. Map of noise measuring sites in Hanoi.
condensed mixture of commercial and residential activities and public utilities. In Hanoi, Sites 2, 6 and 7 are among the busiest roads. Site 2 is a small one-lane street that mainly connects the boundary points of the city without crossing the city’s central zone. One of the biggest universities (Hanoi University of Medicine) is located here. The street of Site 6 mainly connects the boundary points of the city’s central zone and is therefore busy most of the time. The streets of Sites 4 and 7 link the city center with the western and northern highways, respectively. They therefore endure remarkably heavy traffic, which includes motorbikes and cars during the day and heavy vehicles at night. The situation is almost the same for Sites 4 and 7 in Ho Chi Minh City, whose streets link the central zone of the city with the highway that leads to the western suburbs. Among all the sites, Site 7 is one of the most densely populated areas. The street of Site 6 is the narrowest, compared to those in other sites, but its volume of traf-
fic is remarkably high because it offers a shortcut from the city to the western highway. In Kumamoto, two sites were selected. Site 1 is a narrow twolane street where a university (Kumamoto University) is located. Site 2 is a bigger four-lane street connecting the boundary points of the city without crossing the city’s central zone. 2.2. Noise measurement Our acoustic surveys were conducted in September 2005 and September 2007 in Hanoi and Ho Chi Minh City, respectively. The measurement sites in Hanoi and Ho Chi Minh City are displayed in Figs. 2 and 3, respectively. A 24-h noise measurement was conducted at a reference point 1.2 m above ground, and 1–12 m away from the road shoulder by means of sound level meters (Rion NL06 and NL-22). A-weighted sound pressure levels were measured
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Fig. 3. Map of noise measuring sites in Ho Chi Minh City.
Table 1 Traffic volume in Hanoi, Ho Chi Minh City, and Kumamoto.
Hanoi Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7
Number of lanes
QM
QC
QH
% of QM
% of QC
% of QH
QM + QC + QH
4 1 4 6 4 4 6
87,184 137,785 73,981 77,597 89,814 166,610 182,032
14,968 9502 5399 5699 4063 10,829 16,559
2668 1496 543 531 1360 5435 1403
83 93 93 93 94 91 91
14 6 7 7 4 6 8
3 1 1 1 1 3 1
104,819 148,783 79,922 83,827 95,237 182,874 199,994
116,429
9574
1919
91
7
2
127,922
33,444 67,359 156,060 156,096 131,196 73,584 239,031 201,924
198 590 7584 6816 5472 2208 13,773 11,064
12 407 936 2580 3468 792 4974 5496
99 99 95 94 94 96 93 92
1 1 5 4 4 3 5 5
0 1 1 2 2 1 2 3
33,654 68,356 164,580 165,492 140,136 76,584 257,778 218,484
132,337
5963
2333
94
4
2
140,633
3030 3486
19,236 44,628
1020 2700
13 7
83 88
4 5
23,286 50,814
Average
Ho Chi Minh City Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7 Site 8
1 1 2 4 4 1 2 4
Average
Kumamoto Site 1 Site 2
2 4
every second for 24 h. Additional noise measurements at 10-min intervals, together with noise recordings, were conducted at seven sites in Hanoi and eight sites in Ho Chi Minh City in order to obtain data for frequency analysis. During the 24-h noise measurement, traffic volume by vehicle type was also monitored by video camera. The sampling time interval was 10 min in each hour. Traffic quantification was performed later after reproduction of the video recording. Traffic flows were grouped into three vehicle categories: QM = motorbikes, QC = cars/light trucks, and QH = heavy vehicles.
Noise measurements in Kumamoto were conducted at the two selected sites in June 2007 applying the similar method that was used in both Vietnamese cities. 3. Results and analysis 3.1. Traffic volume characteristics Table 1 presents the traffic data collected from each site in Hanoi, Ho Chi Minh City, and Kumamoto. Since QM in Site 2 in
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Fig. 7. Motorbike volume data from Ho Chi Minh City spanning 24 h. Site 2; Site 3; Site 4; Site 5; Site 6; Site 7;
Fig. 4. Hourly traffic volume data from Site 2 in Hanoi.
Site 1; Site 8.
Fig. 8. Sound level fluctuations at 17:00. - - - Kumamoto data (Site 2); — Ho Chi Minh data (Site 5). Fig. 5. Hourly traffic volume data from Site 5 in Ho Chi Minh City.
Fig. 9. Hourly noise levels of Site 2 in Hanoi.
Fig. 6. Motorbike volume data from Hanoi spanning 24 h. Site 3; Site 4; Site 5; Site 6; Site 7.
Site 1;
Site 2;
Hanoi and Site 5 in Ho Chi Minh City are relatively equivalent to the average number of motorbikes in both cities, the overall results from these two sites are considered as representative illustrations throughout Section 3. The daily average number of vehicles from all sites is estimated at about 128,000 vehicles in Hanoi and 140,000 in Ho Chi Minh City. While QM plays the most significant role in the traffic of both Vietnamese cities, QC is found to be more common in Kumamoto, accounting for >80% of the city’s total traffic. On average, 91% of the total traffic in Hanoi is accounted for by
motorbikes, as is 94% of the total traffic in Ho Chi Minh City. Examples of the collected traffic flow data for Site 2 in Hanoi and Site 5 in Ho Chi Minh City are reported in Figs. 4 and 5, respectively, where time variations in the hourly traffic volume are plotted for each vehicular group. In both figures, QM is reflected in the left axis and QC and QH in the right axis. Both cities exhibit an almost similar trend in which there is more QM and QC during the day, and less QM and QH at night or in the early morning hours. In terms of heavy traffic, in Ho Chi Minh City, an increase in QH can be observed during the noon-time hours, which remains the same for every site. In Hanoi, QH is much less compared to QM and QC at Site 5. Nevertheless, at other sites in Hanoi, QH increases slightly during the night time.
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Fig. 12. Relative cumulative frequency of noise levels at Site 2 in Hanoi and Site 5 in Ho Chi Minh City, compared with Site 2 in Kumamoto, Japan.
Fig. 10. Hourly noise levels of Site 5 in Ho Chi Minh City.
Fig. 11. Hourly noise levels of Site 2 in Kumamoto. Fig. 13. 1/3-Octave-band frequency analysis of Site 2 in Hanoi and Site 5 in Ho Chi Minh City, compared with Site 2 in Kumamoto, Japan.
Table 2 Noise levels in Hanoi, Ho Chi Minh City, and Kumamoto. Noise metrics (dB)
LAeq,day
LAeq,night
LAeq24h
L1
L5
L10
L50
L90
L95
L99
Hanoi Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7
76 72 76 74 69 71 77
72 66 71 69 65 65 76
75 71 75 73 68 70 77
84 81 85 82 75 79 85
79 76 79 76 72 74 81
77 73 77 75 70 72 79
73 68 72 70 67 67 75
61 54 59 60 54 56 68
55 49 53 55 49 51 64
48 46 45 49 43 47 58
Ho Chi Minh City Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7 Site 8
74 77 78 72 76 78 76 78
69 72 74 68 71 71 73 76
72 76 77 71 74 76 75 77
81 85 85 79 82 86 83 86
77 80 81 75 79 80 79 81
75 78 80 74 77 79 78 80
70 73 76 70 73 74 74 76
57 61 66 62 64 65 67 71
52 56 61 58 61 64 64 69
47 50 53 52 55 60 59 64
Kumamoto Site 1 Site 2
70 70
66 67
68 69
76 77
73 74
71 73
65 66
51 53
45 49
37 42
Figs. 6 and 7 present data regarding the volume of motorbikes in Hanoi and Ho Chi Minh City, respectively. In both cities, the maximum amount of QM was observed in the morning and evening rush hours, and the least density of QM was observed from 01:00 a.m. to 06:00 a.m. The site-by-site variation in QM in Ho Chi Minh City is greater than in Hanoi due to the fact that Sites 1, 2, and 6 in Ho Chi Minh City were smaller one-lane streets compared to the rest of the sites.
3.2. Noise exposure Since the traffic noise patterns in Hanoi and Ho Chi Minh City are nearly identical, a representative noise pattern from Ho Chi Minh City was taken to compare with a noise pattern from Kumamoto. Fig. 8 presents the level of random sound fluctuation obtained in a 300-s timeframe at Site 5 in Ho Chi Minh City, and at Site 2 in Kumamoto. The noise levels in Ho Chi Minh City fluctuate
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Table 3 Results of noise levels with and without horn sounds for Hanoi and Ho Chi Minh City. Noise metrics (dB)
Site 1
Site 2
Site 3
Site 4
Site 5
Site 6
Site 7
Hanoi LAeq,10 min LAeq without horn sound LAeq difference LAeq horn sound % of time occupied by horn sound
68 67 1 75 8
69 65 4 77 12
67 66 1 63 5
68 67 1 64 9
66 65 1 59 4
66 63 3 63 6
68 66 2 63 9
– – – – –
Ho Chi Minh LAeq,10 min LAeq without horn sound LAeq difference LAeq horn sound % of time occupied by horn sound
73 73 0 78 4
74 74 0 81 2
67 66 1 75 5
66 65 1 72 4
67 67 0 74 4
71 70 1 75 9
69 67 2 75 12
68 67 1 74 5
by approximately 10 dB, with frequent sharp peaks due to audible horn sounds, which indicates that the traffic noise in this city has an impulsive, percussive character. This is different from the sound levels in Kumamoto, which vary by as much as 20 dB, but in which the traffic noise level increases and decreases in a predictably periodic signal pattern. Examples of the measured acoustic data are reported in Figs. 9– 11, where the time variation in the A-weighted sound level Leq and in the percentile sound levels L1, L10, L50, L90 and L99, are plotted for Sites 2, 5, and 2 in Hanoi, Ho Chi Minh City, and Kumamoto, respectively. In Table 2, the average values of the noise levels for all sites investigated in the three cities are also listed. In the overall monitoring sites in Hanoi and Ho Chi Minh City, the daily average noise levels LAeq,day were >69 dB. In general, it was clearly observed that the noise levels in Hanoi and Ho Chi Minh City were higher than those in Kumamoto. In Figs. 9 and 10, the time variation in noise levels is almost the same for Hanoi and Ho Chi Minh City. In these cities, the percentile level L1 is obviously quite high, as it was determined by the emission of horn sounds. In Kumamoto, the L1 level did not vary much over 24 h, and the difference between L1 and L10 was smaller than the corresponding values of the difference in both Hanoi and Ho Chi Minh City. Percentile sound levels L90 and L99 can be considered as background noise levels. A decrease in background noise levels could be detected at night in both Hanoi and Ho Chi Minh City, although the decrease was more pronounced in Hanoi. In Kumamoto, the background noise level was found to be quite low. An example of the relative cumulative frequency of noise levels at Sites 2 and 5 in Hanoi and Ho Chi Minh City, respectively, is shown in Fig. 12, in comparison with traffic noise levels at Site 2 in Kumamoto. It can be seen that the traffic noise in Kumamoto is approximately 5-dB lower than that in Hanoi, but about 10 dB lower than that in Ho Chi Minh City. It is also worth noting that due to horn sounds, the slope of the curves for Hanoi and Ho Chi Minh City is steeper than that for Kumamoto.
3.3. Frequency analysis Fig. 13 compares the results of 1/3-octave-band frequency analysis in Hanoi and Ho Chi Minh City with corresponding results obtained for Kumamoto. Visible peaks can be observed at the lowfrequency range from 80 to 160 Hz in all three cities. The peaks at 125 Hz may be due to noise emitted by motorbike engines in Hanoi and Ho Chi Minh City, and the peak at 80 Hz in Kumamoto may be attributed to car engines. At 3.15 kHz, another two peaks could be detected in Hanoi and Ho Chi Minh City, which were probably caused by horn sounds.
Site 8
3.4. Effect of horn sound on noise exposure From the above findings, it is notable that traffic noise in Hanoi and Ho Chi Minh City has an impulsive, percussive character that is mainly due to frequent horn sounds. At a maximum, horn sounds occupied 12% of the total measurement time in both cities (see Table 3). In order to examine the possible effect of horn sound on noise exposure, the horn sounds were removed from the obtained LAeq,10 min. Table 3 presents results showing that traffic noise in Hanoi decreases by at least 1 dB after horn sounds are removed, while traffic noise in Ho Chi Minh City decreases by 0.7 dB on average. The effect of horn sounds was found to be slightly more pronounced in Hanoi than in Ho Chi Minh City. Although horn sounds contribute a relatively small amount to the total noise exposure, their psychological impact may be greater because of the startling effects of such noise. In a paper investigating the impact of horn sounds on two groups of Vietnamese and Japanese subjects, Phan et al. [8] found that horn sounds had a severe effect on the Japanese subjects and created great annoyance within the group. With regard to the role of impulsive sounds in international standards, the newly revised version of ISO R 1996 [9,10] recommends a 5-dB penalty for impulsive noise, while another study suggests penalties of 10 dB [11]. Thus, in order to predict the community response to traffic noise in cities such as Hanoi and Ho Chi Minh City, it is necessary to investigate the relationship between horn sounds and annoyance. 4. Conclusion Our acoustic surveys in Hanoi and Ho Chi Minh City revealed that in cities of a developing country, environmental noise levels due to traffic are notably higher than those in a developed country such as Japan. Moreover, while cars are the common form of transportation in developed countries, motorbikes are by far the dominant vehicle in the traffic in Vietnam. In general, high noise levels are the result of frequent horn sounds, especially in Hanoi. From our overall site monitoring, the daily average noise levels LAeq,day were >69 dB. The current study is intended as a first step toward determining the characteristics of traffic noise in two major Vietnamese cities. In future studies, we aim to provide fundamental data on the physical characteristics of current noise pollution and to evaluate the population’s response to this increasingly detrimental phenomenon. Acknowledgements This study has received the joint financial support of the Core University Program that includes the Japan Society for the Promo-
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tion of Science (JSPS), the National Center for Science and Technology (NCST), Grant-in-Aid for Scientific Research (Project No. 17560533), and a Kajima Foundation Research Grant (2006). The authors highly appreciate the insightful academic advice on the conducting of noise measurement given by Professors P.N. Dang, L.V. Nai, and P.D. Nguyen of the Hanoi University of Civil Engineering, and by Ms. N.T. Bich Ngoc of the Ho Chi Minh University of Architecture. The authors would also like to thank the students of the Hanoi University of Civil Engineering and Ho Chi Minh University of Architecture for their vital assistance in the maintenance of equipment during measurement proceedings. References [1] Davies H, Van Kamp I. Environmental noise and cardiovascular disease: five year review and future directions. In: Proceedings of ICBEN 2008; 2008. [2] Finegold LS, Harris CS, von Gierke HE. Community annoyance and sleep disturbance: updated criteria for assessing the impacts of general transportation noise on people. Noise Control Eng J 1994;42(1).
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[3] Miedema HME. Annoyance caused by environmental noise: elements for evidence-based noise policies. J Soc Issues 2007;63(1):41–57. [4] Noise abatement and control: department policy, implementation responsibilities, and standards. Washington, DC, US Department of Housing and Urban Development Circular 1390.2 (August 1971). [5] Berglund B, Lindvall T. Community noise—document prepared for the World Health Organization. Arc Center Sens Res 1995;2:86–103. [6] Environmental Protection Agency 1978 EPA Document, November, 550/9-79100, USA Protective noise levels. [7] Commission of the European Communities, Directive of the European Parliament and of the Council relating to the Assessment and Management of Environmental Noise, COM (2000) 468 final. [8] Phan HAT, Yano T, Phan HYT, Sato T, Hashimoto Y. Annoyance caused by road traffic with and without horn sounds. Acoust Sci Tech 2009;30(5):327–37. [9] ISO Acoustics 1996-1:2003. Description, measurement and assessment of environmental noise – part 1: basic quantities and assessment procedures. Geneva: ISO; 2003. [10] ISO Acoustics 1996-2:2007. Description, measurement and assessment of environmental noise – part 2: determination of environmental noise levels. Geneva: ISO; 2007. [11] Groeneveld Y, de Jong RG. CEC joint project on impulse noise: overall results of the field survey. In: Proceedings of internoise 1985; 1985 p. 905–8.