BACKGROUND TO NEW NOISE MAPS FOR STANSTED

The maps produced by the Department for Transport (DfT) to show the areas supposedly affected by noise from Stansted Airport greatly understate the extent of the problem, both now and in the future. The DfT has used the 57 dBA Leq contour line to mark the area within which it says there will be annoyance. (This contour line indicates the area within which the daytime noise levels are, averaged over a year, higher than 57 decibels.) However the World Health Organisation (WHO) drawing on research from all round the world, states that the level should not exceed 50 dBA Leq 'to protect the majority of people from being moderately annoyed during the daytime'.

SSE asked the DfT to produce maps showing the areas affected by 50 dBA Leq, but they refused; so we asked them to give us all the input figures which used in their own computer program, so that we could use noise mapping software to produce our own maps at the 50 dBA Leq level.

This work is very time consuming and our efforts are ongoing. We will gradually be putting more results onto this site, so keep visiting to see the REAL picture of the noise nuisance in store if the expansion goes ahead.

It is important to remember that even our more realistic noise contours can give a false sense of security: a 50 dBA Leq contour line cutting through, say, Harlow doesn't mean that one side of the street will get disturbance while the other side won't. Even being well outside the contour lines is NO indication that you will not be disturbed by the massive onslaught of noise from the huge increase in numbers (and size) of aircraft using Stansted if expansion takes place.

Finally and most importantly, we stress that we do NOT accept that the use of dBA Leq noise contours is an adequate method for representing the likely effects of noise disturbance. This is mainly because it uses a system of measurements which are averaged over the whole of a long period, with the periods of silence counteracting the periods of disturbance. In the real world, we know that aircraft noise nuisance just doesn't work like that. More details of this, and our other objections to the Leq metric may be found in our consultation response.

OUR METHODS

We have used the US Federal Aviation Authority's INM (Integrated Noise Model) software to produce our noise contours, using the number of flights, aircraft types and departure routes as supplied by the DfT and used by them in their own maps. We derived our arrivals routes from recent radar printouts showing where arriving aircraft ACTUALLY go, as opposed to the DfT's unrealistic assumption that all inbound aircraft line up with the runway when 30 miles or more distant. This has a significant impact on the shape of noise contours. In particular, the familiar picture of two fingers stretching north east from the airport is replaced by a shorter, but more widespread area.

In tests to calibrate the DfT's own software, the Civil Aviation Authority concluded that the INM software (as used by us) tends to understate the size of the areas affected by noise compared with the DfT's software. It is likely therefore that all areas shown in our maps are understatements of the areas likely to be affected.

In addition, we have based our maps on the 50 dBA Leq level recommended by the WHO although several international bodies recommend that calculations of noise annoyance in rural areas should use lower levels than urban areas because of the lower background noise levels in the country (ie aircraft noise, for example, will be more likely to be lost in an urban area). These international authorities recommend an additional 'allowance' of 5 to 10 decibels for rural areas. At just 2 decibels quieter (ie 48 dBA Leq), our noise maps show an increase of approximately 50% in the areas affected, when compared to the 50 dBA Leq maps. We are not however publishing these maps, as the exact positioning (as opposed to the actual area) of lower and lower contours is increasingly subject to variations in the assumed flightpaths. The DfTconsultation papers contain insufficient data for us to be sure that these flightpaths would be accurate.

We will soon be including estimates of the numbers of people within the 50 dBA Leq contour, which will be obtained from industry leading information provider CACI Ltd; these figures will be based on more up to date figures than those used by the DfT in their Consultation Documents, where the figures were only updated to 1999.

While taking every care possible, we must state that the production of these maps is a complicated procedure and the results are our best estimates, and are in any case based on a number of assumptions by the DfT. In addition, the usage of flightpaths can and does change and this in turn would affect the noise contour maps.

NEW TYPE OF NOISE MAP

We have also introduced an innovation that we believe is long overdue. Those familiar with the operation of Stansted Airport will know that the direction of take off and landing is dependent on the wind direction. The long term average pattern is for takeoffs and landings to be in a south westerly direction for about 76% of the year and north easterly for the remaining 24%; all Leq noise maps, such as those used by the DfT, average this yearly pattern into a single overall picture. This means that in the maps the bad times when you are getting flights over you are 'watered down' by the inclusion of the periods when you are not getting flights passing over you. We have therefore produced additional maps which show the picture on the days when you ARE getting the traffic. In other words, we have modelled the two areas each getting 100% of the flights rather than 76% or 24% respectively. (Further notes on interpretation are to be found with the relevant maps).

SUMMARY RESULTS

(all figures rounded to nearest whole number)

In summary, our research shows that on the current scale of operations in June 2003, the estimated area bounded by the 50 dBA Leq contour (the WHO recommended maximum for avoiding noise annoyance) covers approximately 76 square kilometres/29 square miles, nearly 2½ times the 32 square kilometres/12 square miles for the 'area of annoyance' reported in the 2002 Noise Exposure Contours for Stansted Airport report published by the DfT.

In the maximum expansion scenario (4 runways, year 2030), the 50 dBA Leq contour encircles 619 square kilometres/239 square miles, over 2½ times the DfT's area of 228 square kilometres/88 square miles.

However this is based on the DfT's way of working out the area on a composite, average basis. Splitting the maps, as described above, gives more informative results. This process of separate mapping of the two modes of operation (i.e. north easterly and south westerly) shows that, in the 4 runways, year 2030 scenario:

*  On the map based on south westerly operations, 519 square kilometres/200 square miles would fall within the WHO's 50 dBA Leq "annoyance" contour; this area would suffer on an average of approximately 3 days in 4;

*  On the map based on north easterly operations, 586 square kilometres /226 square miles would fall within the WHO's 50 dBA Leq "annoyance" contour; this area would suffer on an average of approximately 1 day in 4;

*  These two areas of annoyance overlap in an area of approximately 265 square kilometres/102 square miles, where the majority of residents could expect to be annoyed every day of the year;

*  In total, 840 square kilometres/324 square miles would be affected for longer or shorter periods, depending on the direction of take-offs and landings - over 3 1/2 times the area which the DfT says would be affected;

*  This way of looking at the affected areas shows that the all-in-one composite maps omit a considerable proportion of the numbers of people who would be affected by unacceptable levels of noise for parts of the time.  

Once again, we stress our contention that virtually any Leq noise map will misrepresent the true extent of noise nuisance and, in addition, our INM produced maps are likely to be understating the areas affected.

The detailed results relating to the various possible expansion scenarios can be seen by clicking on the maps below.

DETAILED RESULTS - THE MAPS

Map 1 - This map shows the projected noise contours in 2030 if 4 runways were to be built.

Map 2 - This map shows the effects on the days when departing aircraft would be taking off towards the north east, and arriving aircraft approaching the runway from the south west for 4 runways in 2030.

Map 3 - This map shows the effects on the days when departing aircraft would be taking off towards the south west, and arriving aircraft approaching the runway from the north east for 4 runways in 2030.

Map 4 - This map shows the two split modes of operation recombined for 4 runways in 2030.