Land transport noise is defined as noise arising from vehicles travelling on road and rail corridors and consists of a number of components. The need to effectively manage the noise effects associated with land transport activities is gaining prominence due to a range of factors, including:
- increased private vehicle use
- a greater number of vehicles and increasing traffic densities
- increased proportion of trucks and service vehicles
- changing travel patterns (ie, vehicles are on the road for more hours of the day and night, not just peak hours)
- growing population
- increasing population densities in most urban centres (particularly around transport nodes)
- increased community awareness of adverse factors in the environment.
The characteristics of sound determine the level of noise and its effects. Sound radiates from vehicles in waves. As sound makes contact with surfaces and objects it is refracted, reflected or absorbed. Noise levels decrease by half for every doubling of distance from the source.
Road transport noise consists of two key components: engine noise and tyre/road interaction. Engine noise arises from various mechanisms including the cooling fan, vehicle transmission and exhaust system. Faulty or modified exhausts and vehicle-braking systems in heavy vehicles are also a common source of noise.
Rail noise is created in a similar way to road transport noise. Train wheels, track vibration and engine mechanisms are the key components. Rail noise is also influenced by auxiliary equipment such as brakes and ventilation systems. Train frequency, speed, train type and infrastructure (such as curves and turbulence) also determine noise emissions.
Land use information and projections contained in regional land transport strategies, corridor plans prepared by New Zealand Transport Agency and specific studies commissioned by local authorities can play a useful role in helping identify the noise related impacts associated with these factors.
There are three stages in which the effects of land transport noise can be addressed. These are:
- reducing noise at the source
- reducing the transmission of noise
- avoiding or mitigating noise at the receiving end.
The primary focus of this note is on the last of these stages.
Land transport noise is predominantly experienced along major road corridors, particularly in built up, urban areas, and residential areas near road corridors.
Interestingly, road transport noise is considered to cause greater annoyance than rail noise. Unlike vehicle noise people appear to become accustomed to railway noise exposure and annoyance decreases over time. Although not as prominent an issue as road transport noise, noise associated with the movement of passengers and freight by rail also needs to be considered and managed.
Exposure to land transport noise can affect the health of people and communities, ranging from general interference with everyday activities through to more significant health issues. Excessive noise creates stress-type responses. The most common issues arising from exposure to noise is the interruption of speech, decreased concentration and sleep disturbance. Noise affects people in different ways and creates various reactions depending on the level of noise, the timing and the activities individuals are engaged in. Average noise levels above 65 dBA are highly undesirable.
Effects rise in tandem with the level of noise and length of exposure experienced. Noise exposure can also have temporary or permanent impacts on psychological and physiological functions. Acute noise exposure activates the nervous and hormonal systems leading to increased blood pressure, increased heart rate and the narrowing of blood vessels. After prolonged exposure susceptible individuals may develop permanent effects such as high blood pressure.
Land transport noise can also particularly affect activities that are sensitive to noise interference. Equally, such activities can have a reverse sensitivity affect on the nature and scale of operations within road and rail corridors.
Examples of sensitive activities include teaching, which requires communication and interaction through speech, and sleep, which generally requires peace and quiet.
Sensitive receivers have been defined as:
- residential activities
- education activities including pre-schools
- travellers accommodation
- hospitals and other healthcare facilities
- elderly person's accommodation.
International definitions extend this to include places of worship and areas preserved for their quiet value, such as parks and reserves. The World Health Organisation (WHO) noise guidelines on community noise recommend noise levels for sensitive activities.
Reverse sensitivity refers to the effects of sensitive activities on nearby existing activities, for example road and rail corridors, and can lead to restraints on those activities. Noise is a key reverse sensitivity issue. When a new land use is established near a road or railway corridor the new land use may be affected to some degree.
Land use planning can address reverse sensitivity by restricting certain land uses near existing or planned road and rail corridors and placing conditions, where appropriate, on resource consents.
The WHO noise guidelines provide guidance levels for different activities and environments. The WHO levels are very low and are significantly exceeded in many environments. WHO recommend internal noise levels below 35dBA Leq for speech comprehension. For outdoor living areas in residential areas exposure levels should not exceed 50 55dBA Leq, and in internal sleeping areas =30dBA Leq (8hr) is recommended. Internationally, these levels have not been adopted for the design or management of land transport corridors, as these levels may be unachievable in areas next to major land transport corridors. This demonstrates the need for early land use planning to avoid exposing people and communities to excessive noise levels.
Satisfactory and maximum values are also included in AS/NZ 2107:2000 Acoustics Recommended Design Sound Levels and Reverberation Times for Building Interiors. The standard prescribes slightly higher levels of 30 to 40dBA Leq (8-hr) for sleeping areas on 'major' roads compared with 30 to 35dBA Leq (8-hr) in bedrooms near 'minor' roads. Like the WHO guidelines, these standards include recommended values for a variety of rooms and building uses.
In summary, there is a variety of guidance, particularly describing levels at which health effects are very unlikely to occur. To date no explicit national noise criteria have been developed. There is also no common international standard for roads or railway lines - most countries appear to base decisions on their local context, tempered by what is affordable. Typically, criteria for designing new infrastructure are more stringent than for managing existing infrastructure, however non-regulatory methods may be available to help manage existing noise.