The Mayor's Ambient Noise Strategy - Greater London Authority

122 Mayor of London
The Mayor’s Ambient Noise Strategy
them more noticeable on flightpaths. The number of people and the area
bounded by the Government’s ‘official’ 57 dB L Aeq, 16 hour
noise contour has
fallen (see Figure 16). The contour relates to average daily aircraft
movements between mid June and mid September during 16 hour period
from 0700-2300 hours. The index used in the contour incorporates an
‘energy averaging’ of sound. Many people, including the Heathrow fifth
terminal Inquiry Inspector, believe the index to give insufficient weight to
the increasing number of movements (see box 40 and paragraphs 4C.41-
2). The criticism is that energy averaging over 16 hours does not reflect
people’s experience of specific noise events.
Figure 16 Heathrow aircraft movements, population and area within 57 dB
L Aeq, 16 hour
‘actual modal split’ contour
700.0
600.0
57dBA Population (thousands)
500.0
Total annual movements (thousands)
400.0
300.0
200.0
Dotted lines include Concorde at 1999 traffic levels
57dBA Area (square kilometres)
100.0
0.0
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002
Year
source: Department for Transport - Noise Exposure Contours for Heathrow Airport 2002 8
Box 40: Aircraft noise contours and indices
The 57 dB L Aeq, 16 hour
noise contour has been used by the Government as
an indicator of the ‘onset of significant community disturbance’ 9 . The
Government publishes noise contours, at 3 dB intervals between 57 and
72 L Aeq
, for Heathrow, Gatwick and Stansted. The contours are based on
aircraft movements over the 3 month period 16 June to 15 September.
Many other airports publish similar information. The use of such contours
as an aggregate measure to represent a complex mix of events for
planning and other purposes should not be taken as implying that no-one
outside, for example, the 57 L Aeq
contour is affected. Planning Policy
Guidance Note 24 10 recognised that: ‘Beyond the extremities of the
published contours, noise will still be audible near the arrival and
departure routes.’