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In addition to direct impacts on the environment there can also be upstream and downstream effects. An example of an upstream effect is the emissions from coal-fired power stations producing the electricity to run trains. A downstream effect might be the damage to bushland and waterways from dumping old cars, oil and tyres. In other words, some of the environmental degradation caused by transport takes place outside the area of the transport system.
Loudness
The loudness or intensity of sound is directly related
to the amplitude of the pressure fluctuations transmitted through the air.
The pressure fluctuations cause the ear drum to be flexed and thereby create
the sensation of sound. The ear can sense pressure fluctuations as low as
50 micro Pa (the threshold of hearing) and up to about 5 Pa which is considered
the threshold of pain.
This large range of pressure fluctuation is clumsy
to use in reporting. In addition, as a protective mechanism, the auditory
response is not linearly related to pressure fluctuation. To overcome these
difficulties another unit is used to describe loudness – the decibel (dB).
In outdoor situations a change of 3 dB is required to be noticeable. A change
of 10 dB is generally perceived to be a doubling of the sound level.
Frequency
The human ear can hear a large range of frequencies,
or changes in the rate of pressure fluctuations in the air. The pressure
changes per second, or oscillation per second, have the unit of hertz (Hz).
The ear can detect a range of frequencies from about 20 Hz to 20,000 Hz.
However, not all frequencies are heard equally well with low frequencies
(less than 500 Hz) and high frequencies (greater than 10,000 Hz) being more
difficult to hear.
Duration
A gunshot may be loud but it only lasts a fraction
of a second. Road traffic noise may not be as intense but it is continual.
Therefore measures have been developed to describe how sound varies with
time.
Subjectivity
Individuals have different responses to various sounds.
What one person perceives as music another person may regard as a noise. Unwanted
sound is commonly referred to as noise. Transport noise is a common problem
in urban areas. Noise annoyance is a subjective thing and criteria for noise
control are usually based on attitudinal surveys.
Single loud noises may result in hearing loss and
these noises may need to be controlled from a community viewpoint. However
transport noise is usually of a longer duration and not as loud. Short term
effects are likely to be annoyance or irritation. Transport noise can lead
to problems in emotional well being and cause increased tension by interfering
with sleep patterns or causing disruption to the routines of daily life.
Long term exposure may result in reduced hearing ability.
Noise is generated by the engine and exhaust systems of vehicles, by aerodynamic friction, and by the interaction between the vehicle and its support system (e.g. tyre-pavement interaction for road vehicles and wheel-rail interaction for railway vehicles). Insulation in the engine compartment is used to reduce engine noise, mufflers are used for exhaust noise and pavement type selection may reduce tyre/pavement noise production for road traffic.
The path may also be altered to reduce noise. Increased distance between the source and the receiver results in reduced sound levels due to geometric spreading. It therefore follows that increased path distance results in traffic noise abatement. This abatement measure may be a possibility if sufficient right-of-way widths are available. However the establishment of a green-belt between source and receiver may be a very costly exercise in an urban area.
A more common strategy for noise abatement in urban areas is the use of noise barriers. The barrier is designed so as to reflect and diffract the sound. The difference in noise levels with and without the wall is referred to as insertion loss. Although vegetation is sometimes used as a noise barrier, it is generally found that a more solid, fabricated structure is most effective in noise amelioration.
In some cases it is not practical to mitigate noise in the path e.g. near airports. In these cases it may be possible to improve the situation by insulating the buildings. Measures which can be used include increased insulation of walls and roof, double-glazed windows, acoustic vents and storm doors. These measure are frequently used near large airports, and to protect buildings such as schools near busy roads.
The combustion of fossil fuels for transport use results in the release of several contaminants including carbon monoxide, carbon dioxide, hydrocarbons, oxides of nitrogen, and lead and other particulate matter. Hydrocarbons are the result of the incomplete combustion of the fuel. Particulates are minute particles that are suspended in the atmosphere and include aerosols, smoke and dust particles.
Once emitted into the atmosphere, air pollutants undergo mixing or diffusion, the degree of which depends on topographic, climatic and meteorological conditions. Other pollutants not directly emitted from the source may form in the atmosphere using the directly emitted pollutants as feed material. These include nitrates, sulphates and photochemical oxidants (ozone). Photochemical smog is the result of complex chemical reactions of the oxides of nitrogen and hydrocarbons in the presence of sunlight.
Air pollution can be associated with respiratory damage in humans (bronchitis, emphysema, pneumonia and lung cancer) as well as eye, nose and throat irritations. Societal effects include damage to structures and materials, damage to crops and animals, and atmospheric haze. Global effects from acid rain, global warming and ozone depletion are also of concern.
Fossil fuel combustion, particularly by motor vehicles has been identified as the largest single contributor to atmospheric pollution, particularly in urban areas. Judgement about this must be tempered by the fact that motor vehicles are responsible for most of the urban passenger task and virtually all the urban freight task.
The importance of transport pollution must also be considered in the context of air pollution as a whole. For instance, although cars have higher rates of carbon dioxide emissions per passenger kilometre than buses and rail, motor vehicles contribute less than 25% of total carbon dioxide emissions. The bulk of carbon dioxide emissions come from coal-fired power stations which are usually located well clear of major urban areas. They do however provide the motive power for urban rail services.
The rate of emission and the concentration of particular pollutants is also affected by the speed of road vehicles. Emissions increase markedly when vehicles accelerate and are low when they are idling. The impact of congestion on pollution levels is a complex question but it is widely accepted that traffic congestion increases local air pollution.
Pollution levels at a location vary considerably depending upon the type of vehicle operation, the time of day and the atmospheric conditions. In some cities the peak condition for carbon monoxide concentration follows very closely the chronological sequence of peak-hour vehicle operations, but in other cities this relationship does not occur. Vehicle age is a factor in the level of pollution, primarily because of innovations in anti- pollution equipment.
In addition to these considerations, other ecological considerations are required. Coastal zone management must be considered if the project is located near a coastline. The effects on agricultural production must be considered if the project goes through or is adjacent to arable land. If the project is in a floodplain special considerations will be required. It becomes apparent that ecological impacts are very important and that many players will need to be involved during the planning stage.
The requirements for environmental documentation vary depending upon the different legislative and procedural arrangements adopted by differing governments. Most however have the following common features:
It is now usual for the public to be involved in the basic decision-making process. Involvement of the public from an early stage is desirable in order to minimise major conflict after a project is committed or has reached a stage where modification is difficult. The essential aspect is that public comment should be initiated before a commitment is made to the project so that it is publicly evident that comments have the potential to influence the course of the project.
The evaluation of EIA documents is carried out by the appropriate authorities both as an aid to government decision making and to enable the identification of any environmental conditions which need to form part of the approval.
Subsequently it was found that some of the energy from the sun that had been absorbed by growing plants was retained when the plants died. The dead vegetation was transformed over a long period of time into fossil fuels such as coal and oil. Developments in the Industrial Revolution showed that these fuels could be utilised to provide motive power via steam and internal combustion engines.
Throughout the twentieth century the majority of the world’s population has become dependent on the use of fossil fuels to keep industry and communication going. Transport in particular has come to rely almost exclusively on liquid fuels derived from crude oil. This is because these liquid fuels are convenient and economical to use, and because their energy content (in terms of energy per unit mass of fuel) is much higher than alternative fuels.
However, the fuels on which we currently place so much reliance are nonrenewable and are being rapidly depleted. There is therefore a need for society to conserve energy, to develop alternative energy technologies, to increase the efficiencies of various components of society’s infrastructure (particularly transport), and to improve its understanding of energy issues.
Spatial structure refers to the order and relationship among physical elements and land uses. This structure evolves over time from the interaction among individuals, households, firms and institutions. Land use planning generally uses a prescriptive approach in deciding what future spatial structure should be developed. This prescription is based on a land-use arrangement that is most efficient and least costly to government and its citizens, considering elements such as health, safety, convenience, environmental quality, social equity and social choice. In recent times, studies relating to energy-efficient patterns of land development have assumed importance.
Energy efficiency is a special case of cost efficiency. The transport sector is a heavy consumer of fuel, and it can be concluded that land-use alternatives which minimise travel are usually fairly energy efficient solutions in the use of land. Another consideration is the development intensity which is used for land. For example a city that suffers from urban sprawl and ribbon development will have more kilometres of streets and services (water pipes, sewer pipes, electricity cables, etc.) than would a more compact city. In this case initial development costs will be higher, but so will the cost of ongoing maintenance and replacement. In reality, the crucial issue is the costs the citizens are willing to pay in order to satisfy their wants. This willingness to pay is a function of a society’s values, attitudes, and preferences.
Energy Demand
Energy use may be thought of as occurring in four basic sectors: transport, residential, commercial and industrial. Transport accounts for a significant proportion of total energy use in most industrialised countries. Public policy in Australia has been to provide relatively cheap energy and social, community and industrial development has progressed on this premise from the end of World War II (1945) until recent times. This has been one factor that has contributed to urban expansion in Australia. Other factors include rapid increase in real per capita income, rapid diffusion of the car, development of the major road system in preference to the development of public transport, and land-use planning policies which have encouraged low-density residential development. However changes in factors such as the decline of household size, new environmental controls and energy policy are now occurring which could change this pattern in the future. Transport uses about 30% of the energy used in Australia. About one third of that (10% of the total) fuels urban car travel. If the urban car usage could be halved some increase in public transport energy usage would occur, but an overall reduction of about 3% of national energy use may be possible. This is just one way in which our national energy use could perhaps be reduced. The challenge is for society to be willing to tackle the hard decisions involved in reforming our energy usage.
A major area for potential saving is the transport sector. A great deal of investigation and research has been carried out in recent times to consider ways in which transport energy usage may be reduced. The solutions proposed are quite varied, and the following presents just a few of the ideas which have been investigated or are being implemented:
Environmental Principles for Engineers (Institution of Engineers, Australia 1992) expands on this description to make it more applicable to the broad scope of engineering works. Important issues with respect to transport planning are:
Economic, environmental and social sustainability are often mutually reinforcing. Road or public transport systems that fall into disrepair because they are economically unsustainable fail to serve the needs of the poor and often have environmentally damaging consequences. Hence, the three types of sustainability are closely linked and a policy on sustainable transport must therefore consider all three aspects in order to be comprehensive and effective.
Page last modified 3 July 2003.