Singapore is a city-state of 5 million people. The entire urban population has expanded from 4.4 million to 5 million in a matter of 5 years. Because of the scarcity of land available, more major roads and expressways are being run close to residential developments, exposing the residents to expressway noise. Recognizing the problems of noise in a high-density urban society such as Singapore, the National Environmental Agency of Singapore (NEA) has set prescribed noise limits for residential areas. The purpose of this paper is to analyze the noise level in one such development that is adjacent to an expressway, examine the effect of building height on noise and to compare the results with the NEA standards. The paper concludes with the implications of the results and a discussion on the solution to the problem.
Keywords: Excessive noise, expressway noise pollution, noise data logging, photovoltaic cells, sound barriers, variance of noise level with height
|How to cite this article:|
Bhanap I. An analysis of roadway noise at residential estates in close proximity to expressways in Singapore. Noise Health 2013;15:183-9
| Introduction|| |
Today, there are many ways in which our environment is contaminated. For example, our air these days can be contaminated with dust, ash and other small particles, a phenomenon known as air pollution. Similarly, the water bodies and land can also be contaminated with harmful, leading to the phenomena of water and land pollution respectively.
But, perhaps, the form of pollution we tend to overlook most often is noise pollution; perhaps because its effects are not as sudden or striking as the other forms of environmental pollution; nevertheless, it is equally dangerous as the other forms of pollution and can cause a string of health complications to people around the world.
Every day, we are all exposed to different sounds in this world. While some are pleasant to our ears, others irritate us. The latter is known as noise. The exposure to irritant or displeasing levels of noise, which may lead to a disruption in human activity is known as noise pollution.
Because of urbanization and the shift in population to the cities, more and more people are exposed to noise, leading to the development of health complications associated with noise, which will be discussed further. Noise pollution these days is mostly experienced in busy cities around the world, such as New York, London, Tokyo and Singapore.
Singapore has transformed itself into a highly developed, economically advanced city-state. All of Singapore's 5 million residents live in urban areas, with almost no rural population.  Land in Singapore is scarce, with an area of approximately only 694 km 2 .  To cope with the increasing population of Singapore, more road networks are being built in Singapore. The road density of Singapore has increased from 447.5 km per sq. km of land to 471 km per sq. km of land from 2003 to 2008.  Due to the limited land, it is inevitable that many residential estates will be developed close to major arterial roads and expressways with high traffic densities.
According to an article in the "Straits Times," as Singapore's economy and population have grown so have public complaints about noise pollution. The government announced in June 2011 that it would study noise along all 65 km of elevated Mass Rapid Transit (MRT i.e., the commuter trains) tracks to identify hotspots and solutions. The Land Transport Authority of Singapore is also co-chairing a multi-agency study on noise with the National Environmental Agency of Singapore (NEA). This second study will look into the noise levels of 60 road and rail locations across Singapore. Noise levels look set to increase as Singapore's population and road traffic rises. There were 951,307 vehicles on the road at the end of June 2011, a 37% jump from 2000. 
In this study, roadway-generated noise is measured throughout the day for a 1-week period and the data logged on a computer for analysis. Noise is measured in the logarithmic scale of decibels (dB). [Figure 1]  below shows the different types of background (ambient) noise we hear and how they are expressed in dB. In the case of sound, as the decibel scale is a logarithmic scale; a sound of 20 dB is nearly 10-times as loud as a sound of 10 dB and not twice as loud. This just shows how much difference there is in the sound from a quiet office and the sound in a bedroom. In this situation, a quiet office is about 10-times louder than a bedroom.
|Figure 1: A standard noise chart equating the loudness of different environmental sounds in terms of decibels|
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Health complications of noise pollution
The effects of noise pollution have been severely underestimated and overlooked. While the complications caused by exposure to excess noise are not as serious as other medical problems, they are known to have caused numerous problems such as the ones listed below. 
How much noise can we sustain
- Productivity: Noise is often known to be distracting and can often interfere with people when they are doing their work. Extensive research has shown that people working in noisy environments tend to be less motivated and have higher stress levels than others working in a relatively quieter environment, as excessive sound is often considered as an annoyance.
- Learning impairment: Noise pollution has also known to have caused learning impairment and reading difficulties in children who were exposed to noise for long periods of time.
- Other health complications: The most serious problem of noise pollution is the health complications it offers. People who are exposed to excessive noise or noise for long periods of time are known to have suffered from problems such as chronic stress, temporary and permanent hearing loss, irritability, hypertension, high blood pressure, stroke and the most obvious one that is sleep disturbance. Research has shown that sleep can be significantly disrupted when ambient noise is 55 dB or higher.
Generally, sound of up to 45 dB is considered the limit indoors as per the United States Environmental Protection Agency (USEPA).  Above 45 dB, we tend to get a little irritated. And, as seen from [Figure 1] below, on different scenarios and the amount of noise generated, 45 dB is a little shy of the amount of sound in a quiet office. However, as the research is being conducted in Singapore, we will adhere to the noise limit set by Singapore's NEA. Here is a table that shows the limit set by the NEA of Singapore on the maximum noise level permitted for a residential area.
| Methodology|| |
The research was conducted in an apartment block in a condominium adjacent to the East Coast expressway. The apartment block is 50 m away from the expressway. The East Coast expressway is a major expressway linking the international airport and the eastern areas of the island with the central business district, port and the west coast of Singapore. The expressway is a 10-lane expressway near the apartment block used for the study and is approximately 37 m wide. 
Noise data was logged using a noise data sensor and data logging software on a Windows laptop [Figure 2]. The noise sensor was mounted near an open window facing the expressway on the 11 th floor apartment and the data logged on the Windows laptop. Noise data was logged from 8:30 am to 10 pm every night for all days of the week. The logging software was set to sample noise data every minute. The software user interface is shown below [Figure 3].
|Figure 2: The noise data logger connected to a laptop via a USB connection for logging|
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Data logging commenced on Sunday, the 7 th of August and ended on Saturday, the 14 th of August.
Data sensor and logging software details
The noise level data logger Standard Model ST-173 consists of a data sensor with a USB connector at the other end [Table 1], [Table 2], [Table 3] and [Table 4] and [Figure 4]a-h. It plugs into the computer through the computer's USB port. Once everything is set-up, the next time the data logger is plugged into the USB port of a computer, the software automatically launches and is ready to record the sound.
|Table 1: The residential noise limits prescribed by the national environmental agency of Singapore at different periods of the day|
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|Table 2: The maximum, minimum and average sound values from Sunday to Monday|
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|Table 4: The quietest and loudest floor in terms of noise level (decibels)|
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| Results|| |
The graphs below show the noise level on Sunday 7 August as well as the noise limits prescribed by the NEA at different times during the day.  The y-axis represents the noise level, measured in dB, while the x-axis represents the time, with intervals at every 0:30 h. (could you kindly also show the noise levels for the other days).
Here are the statistics for the noise level throughout the week represented in the form of a tabular column.
We can observe that the average noise level on a Monday is highest, topping at 73 dB. The quietest day that was observed was a Tuesday, with an average noise level of 70 dB.
How does noise vary with height?
A study was also conducted on how the noise level varies with height and, therefore, the study was conducted in the same block where the previous study was conducted. The research involved going to each floor in the block, logging the noise level for 5 min and taking its mean. Unlike the first data collection, this was done in real time, just to analyze the variance of the noise level with height. Given below is the data in a tabular and graphical form.
Noise level decibels versus floor number
[Figure 5] shows a rapid increase in the noise level as you ascend from the 1 st to the 6 th floor. However, interestingly, the increase in noise as you ascend from the 6 th floor to the 11 th floor is very minor compared with the rapid change from the 1 st to the 6 th floor. Nevertheless, we can observe that the graph of noise level against floor height is linear. Also, interesting to note is that even though the noise level varies with height, it has consistently remained above the prescribed limit, which is a concern.
|Figure 5: The graph of the noise level against the floor number. The y‑axis represents the noise level measured in dB, while the x‑axis measures the floor number|
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Solutions to counter noise
As can be seen by the study, there is clearly a major problem with the amount of noise the residents near expressways in Singapore are exposed to. Throughout the period that has been recorded, the noise level has been above the prescribed limit.
A large number of studies have been done globally on the reduction of roadway noise and from the literature available; it appears that most tend to focus on erecting a suitable sound barrier on the side of the road, such as concrete or earthen walls or planting trees. These are quite adequate where the roads run through low-rise residential estates but are of not much use in high-rise residential areas. As we have seen, the roadway noise level continues to rise with the height of the residence and as such short barriers erected on the side of the expressway or trees provide little or no relief. It is quite obvious in this case that the only way to shield residents from roadway noise is to encapsulate and thereby insulate the expressway in some way. A few solutions already deployed in some major urban centers as well as some novel possible solutions are discussed along with their pros and cons.
The Melbourne sound tube
As shown in [Figure 6]  a giant glass structure built around the western portion of the City Links expressway in Flemington, a suburb in Melbourne, which links the Tullamarine freeway with the central business district in Melbourne.  The aim was to mitigate noise around the portion of the expressway near residential areas. It was designed by Roger Rugless, and is 300 m long, 42.4 m wide and about 8 m in height. In Australia, the government standard for maximum noise is about 63 dB, while before the construction of the sound, the residential areas, especially at the higher floors, experienced noise levels of 70 dB.
Curved and tapering steelplate frames encapsulate the twin roadways. The sound attenuating cladding forms a C-shaped enclosure on one side and roofs over one outside lane of traffic completely. On the other side, cladding rises only a little above the parapet level. 
The green tube
A possible ecologically friendly solution to this problem would be to build a 'green tube' around the expressway as shown in [Figure 7].  Similar to the Melbourne sound tube, it envelops the expressway, but instead of being made of glass, it is made of very strong bamboo. Bamboo is ecologically friendly as it is biodegradable and is also very strong and flexible at the same time. Then, creepers can be grown around this bamboo structure. These creepers will aid in mitigating the noise, as they will absorb most of the sound. A similar structure was presented at the Shanghai Expo by India, which consisted of a large bamboo dome covered with creepers and plants. 
|Figure 7: The bamboo structure of the Indian pavilion at the Shanghai Expo|
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The photovoltaic sound tube
I believe that the same idea that was implemented in Melbourne should be implemented here in Singapore by building noise barriers around major roads and expressways that are adjacent to residential areas. However, instead of simply building a noise barrier to block the noise, solar panels can be placed on top of the sound barrier to generate clean electricity. Because Singapore receives a large amount of sunshine, this solution would be feasible and has a lot of potential. While the transition may not be easy or cheap, generating electricity for using solar energy might offset the costs.
Conclusively, this research has revealed the alarming noise problem of residential areas near expressways and their concomitant health problems. A thorough analysis of the varying levels of sound with height has also been explored and a number of solutions have been proposed that can, if not eradicated, mitigate the noise levels near residential areas.
| References|| |
185 Tanjong Rhu Road, #11-01, Sanctuary Green, Singapore 436924
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
[Table 1], [Table 2], [Table 3], [Table 4]