Nowadays, deterioration of the environment constitutes one of the most important problems that humanity faces. The rapid growth of population, the uncontrolled urbanization of many areas around the globe, and the huge development of human activities has caused not only huge amounts of water and air pollution but also an increase in noise levels in our environment. As an architect and urban designer, I have focused my research on the role that urban design and planning play in the management and mitigation of noise pollution, paying special attention to traffic noise in urban environments, which represents the main source of noise complaints (Garcia 2001, 185).
Effects of Noise on People
Many studies undertaken in recent decades have demonstrated that urban noise exposure can have detrimental effects on people’s health. In 1980, the World Health Organization (WHO) raised the alert about the risks of noise exposure and issued recommendations for the limitation of environmental noise. It recommended a maximum value for noise levels of 55 dB during daytime and 35 dB for nighttime (World Health Organization 1980, 19). Above these levels, noise can produce direct auditory effects such as permanent or temporary hearing loss, as well as other non-auditory effects such as annoyance or stress. Hearing problems associated with high levels of noise in industrial settings long have been proven. As the WHO explained in its report, sound vibrations in the air reach our ear canal, causing the eardrum to vibrate. These vibrations are transmitted to the brain by hair cells into nerve impulses. However, “blasts or other intense or explosive sounds can rupture the eardrum or cause immediate damage to the structures of the middle and inner ear, while hearing loss due to prolonged noise exposure is generally associated with destruction of the hair cells of the inner ear” (World Health Organization 1980, 36).
On the other hand, noise exposure can cause other problems to human beings’ health. Among the non-auditory effects, sleep disturbance acquires special importance due to its long-term effects: modifications to the immune system, effects on the sympathetic nervous system, changes in the secretion of some hormones (particularly growth hormones), increase in the level of blood cholesterol, and risks of chronic cardiovascular disorders (World Health Organization 1980, 15). In addition to this, high noise exposure, such as what occurs among people living near airports, industries, and noisy streets, may have a large temporary or permanent impact on physiological functions. However, the relationship between noise and these health effects is not as evident as in the case of permanent and temporary hearing loss.
Urban Noise Sources
Human activities are the main sources of noise pollution, most commonly in cities . Among all of the noise sources that we can find in our cities, such as airports, industries, or building works, I am going to focus my study on road traffic, since it represents the most important and the first source of noise complaints in developed countries. Moreover, it has been estimated that “about 20% of the population in developed countries are currently exposed to road traffic noise equivalent sound levels (Leq) exceeding 65 dB, measured outside of the building facades” (Garcia 2001, 185). Although urban traffic sources produce lower levels of noise than industries and airports and therefore do not harm the hearing organs, they can be considered the most harmful sources if we take into account the number of people affected.
Traffic noise is determined by a series of factors: the individual noise generated by the vehicles, the vehicular flow, the composition of the traffic, and the section of the street. These factors depend mainly on vehicle technology and urban design: street design, road characteristics, and traffic organization. In vehicles, the engine, transmission system, exhaust, air intake, and tires are primarily responsible for noise generation. Nevertheless, although the automobile industry has improved its technology considerably during recent years, it has made very little improvement related to noise pollution because all of the efforts have been focused on energy consumption and air pollution (Garcia 2001, 186). When considering the individual noise generated by vehicles, we also have to take into account friction and aerodynamic noise. The noise produced by friction with the pavement depends on the kind of pavement and the vehicle’s speed, and it can be reduced, for example, by using a more porous pavement. In addition to friction, speed is also a crucial factor with respect to aerodynamic noise, which acquires special importance at speeds over 50 miles/h.
Vehicular flow has a direct impact on noise pollution, which grows proportionally with the number of vehicles until the flow gets saturated, and then it reduces due to the decrease of speed. In addition to this, the composition of the flow—heavy traffic, public transport, or cars—appears to be a decisive factor. Generally, heavy vehicles are noisier than light ones, but when we refer to public transport, it has been proven that these vehicles are quieter than individual cars transporting the same amount of people (Miyara 2004, 1).
Finally, the morphology of the street influences significantly the reflection and reverberation of noise. The section of the street can be open with no buildings on its sides, allowing sound waves to flow; an L shape, reflecting waves on one side and increasing noise levels; or a U shape, producing a reverberate effect.
Lately, many cities and private entities have developed noise maps with the aim of identifying the most exposed areas. “Noise maps are georeferenced records of noise levels or other relevant acoustic information obtained in a given geographical area” (Miyara 2004, 6). They represent not only a useful diagnostic tool to detect and correct problems but also allow us to develop prospective studies of acoustical impact, which are very helpful in urban planning and infrastructure projects. On the other hand, noise maps are very expensive tools requiring a lot of investment in field work. However, there are some initiatives, such as noisetube.net, that provide the needed tools to measure urban noise for citizens in order to create a public platform for noise measurement and management.
Noise map of the area next to Boston University, Boston [Source: The Sony Computer Science Laboratory. Noise Tube. 2009. http://noisetube.net/ (accessed 07 31, 2009)].