- 1.1 Describing aircraft noise in ‘everyday’ terms
- 1.2 Conventional information—ANEF contours
- 1.3 The role of the ANEF
- 1.4 The Sydney Airport experience
- 1.5 Broad issues
- 1.6 Assessing the total noise load generated by airports
- 1.7 Drawing the information together
Most people who are affected by aircraft noise do not have a technical background and when talking about aircraft noise use ‘everyday’ terminology. For example, they make statements like ‘Three noisy planes flew over my house in the last half hour.’ They do not use, and do not want to use, complicated technical terms when discussing aircraft noise.
Experience has shown that members of the public are interested in being provided aircraft noise information in a form that they can readily relate to. The following are some of the typical questions that are asked. Where will the flight paths be? How many aircraft will use the flight paths? At what time will I get the noise—during the day, early mornings, evenings or weekends? What will it be like on the ‘bad’ days? Will I get more noise in summer? Will the largest and noisiest aircraft fly over my area? Will I get take-offs or landings over my house? When will I get a break from the noise?
Despite these simple questions, it has been conventional until recently for relevant authorities to only provide complicated answers.
In Australia the conventional approach to providing information on aircraft noise has been to publish Australian Noise Exposure Forecast (ANEF) contours. These contours show the amount of total noise energy received by locations on the ground near an airport on an annual average day. Australian Standard AS2021 ‘Aircraft noise intrusion—building siting and construction’ uses ANEF values to determine land use compatibility. For example, the standard states that areas with an aircraft noise exposure level of less than 20 ANEF are ‘acceptable’ for residential development [ref 1]. Appendix A contains a brief description of the ANEF system.
The production of ANEFs is required at leased Commonwealth airports as part of the airport master planning process established under the Airports Act 1996.
To illustrate the way the ANEF system has been used as an information tool it is useful to examine the type of advice that has conventionally been given to a person who is considering moving into a new area and is interested in learning about aircraft noise exposure.
This person has generally been given advice by aviation and/or local government authorities along the following lines:
‘There is an Australian Standard which sets criteria for the siting of houses to protect occupiers from aircraft noise. Under the Standard sites which have an Australian Noise Exposure Forecast (ANEF) value less than 20 ANEF are acceptable for housing. The house you are looking at has a noise exposure of less than 20 ANEF and therefore it is in an area which the Standard says is acceptable’.
Depending on the circumstances this advice may also have been tempered by additional words such as ‘you will be able to hear aircraft noise at the house and if you are very sensitive to aircraft noise you may find that it affects you.’
This approach is illustrated by a 1985 letter from the then Department of Transport to a member of the public which was reported to the 1995 Senate Select Committee on Aircraft Noise in Sydney in which a person was told that ‘…[the house] is situated outside the 20 ANEI [(ANEF)] contour. Aircraft noise is therefore objectively assessed as being insignificant and the area suitable for residential use.’ [ref 2]
At best this advice is not very enlightening—being told that the noise exposure at a house site is less than 20 ANEF does not give the person any sense of what the noise will be like. The advice has only told the person that an Australian Standard (based on ‘expert’ analysis of data on community reaction) has decided that he/she would not be too upset by aircraft noise if he/ she were to move into the house. Indeed, on one interpretation, the person concerned could conclude that no aircraft noise would be heard. Given the statement in an ‘official’ letter that ‘….noise [outside the 20 ANEF contour] is …insignificant…’, it is not surprising that people would form the view that aircraft noise would only be a problem ‘inside’ the contours.
Unfortunately experience in recent years has demonstrated that the aircraft noise problem is not confined to areas inside the noise contours. In fact most complaints about aircraft noise at Australian airports come from people who live outside the published ANEF noise contours (ie the 20 ANEF). This is illustrated in Figure 1.1. At Sydney Airport during 1998 approximately 90% of the complaints came from residents of areas outside the 20 ANEF (ANEI) contour.
The ANEF system was developed and adopted in the early 1980s. Over a period of years the use of ANEF contours as an aircraft noise information tool grew to the point where these contours effectively excluded all other ways of describing aircraft noise exposure patterns. This is despite the fact that ANEF contours were not developed, or initially intended to be used, as a way to describe noise impacts to the non-expert. The ANEF system is primarily a land use planning system.
In recent years there has been much public criticism of using ANEF contour information to describe aircraft noise exposure. Clearly, as described in the previous section, there are shortcomings in the way the contours have been used in the past to provide community information and strategies to address these are a major thrust of this paper. However, this does not mean that the ANEF system has no place or that it should be discarded. Rather its role needs to be more clearly defined and its strengths and weaknesses recognised.
An ANEF at a particular point on the ground is computed by summing up the noise energy received at that point on an average day. The contour maps are based on the ANEF being computed across a grid with the contour lines joining those grid points with equal ANEF value. Technically this is a more complete way to portray the noise exposure at a point on the ground than the ‘user friendly’ indices discussed in this paper.
The underlying approach of the ANEF system—forecasting and reporting aircraft noise exposure through summing total noise energy—is common to that contained in the aircraft noise indices used by most overseas countries.
The study that led to the establishment of the ANEF system showed that, when compared to other noise metrics, the ANEF most closely relates community reaction to noise exposure [ref 3]. Given this, and the fact that it is more technically complete than other metrics (ie it computes total noise dose), it is the most valid way to define land use acceptability for areas around an airport. This of course was the reason the ANEF was established. The above arguments also directly support the ANEF as being the most appropriate metric to use when determining eligibility for insulation under the Sydney Airport Noise Insulation Program.
Given that the ANEF is the most technically complete way of portraying noise exposure patterns there is clear logic in it being used as the basic technical assessment tool in environmental assessments for a project (in particular in Environmental Impact Statements). However, because such assessments often serve a dual role of technical analysis and dissemination of information, and because the decision makers on the project will almost certainly not be noise experts, it is considered imperative that ANEF information in an environmental assessment be supplemented supplemented supplemented supplemented supplemented by other approaches.
In November 1994 the third runway opened at Sydney Airport. The resultant changes in noise exposure patterns, which concentrated noise on suburbs to the north of the Airport, triggered a public outcry which ultimately led to the establishment of the Senate Select Committee on Aircraft Noise in Sydney.
The Select Committee's report was particularly critical of the way in which the noise impacts had been portrayed in the project's Environmental Impact Statement (EIS) [ref 4].
As was standard practice at the time, the EIS had used ANEF information as the prime tool for describing the changes in noise exposure. For a range of reasons a large number of people considered that they had been misled by the way this information had been presented.
In response to the Select Committee's recommendations major changes have now been made to the way in which aircraft noise is described and discussed with the community in Sydney. The conventional approach involving noise experts trying to find easy ways to explain to non-experts what their metrics (such as the ANEF) mean has largely been superseded. The new approaches are based on describing, as far as possible, aircraft noise in a way which a person uses when holding an ‘everyday’ conversation or making a telephone complaint. These are described and discussed in Chapters 2, 3 and 4. These changes have largely evolved over the past three years during the process of developing and implementing the ‘Sydney Airport Long Term Operating Plan’ (LTOP). This Plan also arose out of the Select Committee's recommendations and is designed to remove the concentration of noise over suburbs to the north of Sydney Airport through a ‘noise sharing’ approach.
There are a number of broad issues which overlay the specific problems generated by describing noise to the community simply in terms of an ANEF number.
These have been grouped under the headings of ‘The Average Day’, ‘Sensitive Times’ and ‘Extent of Coverage’ and are areas of difficulty when using any noise metric.
Conventional aircraft noise metrics reduce information on noise exposure to that on an annual average day since this has proven to be the most convenient way to condense the information to a digestible amount. However, aircraft noise exposure for many areas around an airport varies very widely from hour to hour, day to day and season to season and hence an average day is rarely a typical day. Aircraft noise often has ‘flood’ or ‘famine’ qualities.
This means that the information that is given to the public very often doesn't relate closely to a person's actual experience.
The problems generated by reducing noise information to the annual average day were specifically addressed in the report of the Senate Select Committee. A quote from the report encapsulates the issue
‘An average figure for levels of intrusive noise is meaningless; it is usually the peaks which draw the most hostile response. So too an averaging of noise energy received over a year, which will simply mask periods where the intensity is very high…’ [ref 5]
It is generally recognised that at certain times of the day (or the week) an aircraft noise event will have a greater impact. Social surveys and noise complaint patterns indicate that for most people the most noise sensitive times are night-time, evenings and early mornings and weekends.
The ANEF system allows for this to some extent by including a four times weighting for movements between 7pm and 7am. Other systems used overseas have different weightings for different time periods (e.g. the DNL used in the US weights movements between 10pm and 7am by 10 times). By way of contrast the Leq used in several countries has no weighting for sensitive times.The differences in the hours and magnitude of the ‘sensitive times’ weightings is one of the major differences between individual international noise metrics and clearly therefore it is a difficult area on which to reach agreement or to prove that there is a ‘right’ answer.
It was shown in Section 1.2 that under the conventional ANEF approach no aircraft noise information is given to residents of areas outside the 20 ANEF other than that the area is suitable for residential use. The lack of specific information on aircraft noise exposure patterns for these residents was a major area of criticism raised by the Senate Select Committee. The two paragraphs below highlight this point and the position adopted by the Committee.
‘The adoption of land use planning criteria to confine noise impact [the 20 ANEF] meant that residents from as far afield as Ku-ring-gai, Summer Hill, Haberfield, Kurnell and Bundeena were led to believe that they would not be affected by aircraft noise. These residents were effectively disenfranchised by this approach. They took no active part in the EIA process because they felt themselves unaffected.’ [ref 6]
‘It is essential that information concerning noise impact at levels below 20 ANEF be provided to affected communities.’ [ref 7]
The indicators in this paper have therefore placed emphasis on giving information on noise exposure as far away as possible from an airport recognising that the information will be less reliable for areas distant from an airport.
It is frequently necessary for an assessment to be made of the overall changes in noise exposure resulting from, for example, the construction of a new runway or the restructuring of the airspace arrangements at an airport.
Decisions are commonly based on analyses which compare the number of persons within particular noise exposure zones for a number of options. However, analysis of this type of information is not straightforward. In order to address some of the problems identified with current approaches a simplified additional Index—the Person-Events Index—has been developed.
This is discussed in Chapter 5.
This Index is intended to supplement and not replace existing assessment methods.
Some implications of adopting the noise indicators presented in the core of the paper are discussed in Chapters 6. This leads in Chapter 7 to the Department's suggested approach for furthering the use of these indicators.