Rail and wheel roughness - implications for noise ... - ARCHIVE: Defra

AEATR-PC&E-2003-002
ATQ - CRN predictions for the
Lnight (dB)
7
6
5
4
3
2
1
0
-1
0 1 2 3 4 5 6
ATQ - CRN predictions for the L den (dB)
Figure 6-4 Correlation between the ATQ-corrected predictions minus the CRN
predictions for L den and L night
7
Compared with the other variables there is clearly a very close relationship between the ATQcorrected
predictions and the CRN predictions for the L den and the L night . This is probably
because the L den is often dominated by the night time contribution and because both sets of
data are differences rather than absolute levels.
Based on these findings the following single back-end correction to the complete CRN
prediction was derived for all the data.
Correction = 8.33× log10(
v + 21) −15
dB (Above 42 km/h)
Correction = 0 dB
(Below 42 km/h)
Where, v is the average speed of all the individual trains passing the site in km/h
Figure 6-5 shows the back-end correction in graphical form.
7 The data plotted in Figure 6-3 and 6-4 are for the difference between the levels predicted using CRN with an
ATQ correction and those predicted using the standard CRN. This means that although the Lnight does not have
the 10 dB correction used for the night time noise levels in the Lden the data plotted in Figure 6-4 will tend to
pass through the origin.
AEA Technology 31