Newlands Cross Upgrade EIS - European Investment Bank

South Dublin County Council N7 Newlands Cross Upgrade
Environmental Impact Statement
Arup Consulting Engineers
Note that all calculations are performed to one decimal place. For the purposes of comparison
with the design goal of 60dB Lden, the relevant noise level is to be rounded to the nearest
whole number in accordance with guidance given in the NRA document.
3.9.4.4 Input to the Noise Model
The noise model was prepared using the following data:
• road alignments, topographical data and Ordnance Survey mapping supplied by Arup
Consulting Engineers;
• traffic flow data supplied by Arup Consulting Engineers;
• traffic speeds as advised by Arup Consulting Engineers.
3.9.4.5 Output of the Noise Model
Predictor calculates noise levels for a set of receiver locations specified by the user. The
results include an overall level Lden in dB.
3.9.4.6 Calibration
The purpose of noise model calibration is to ensure that the software is correctly interpreting
the input data and providing results that are valid for the scenario under consideration. The
CRTN prediction methodology has itself been previously validated.
Given the nature of the scale of the Scheme in question, it was decided that the most
appropriate mechanism for calibration would be to compare the output of the Predictor model
with the output of another CRTN package, i.e. the National Physical Laboratory’s (NPL) html
utility.
The input data for a number of critical receptors was retrieved from the Predictor model and
input to the NPL utility. The results from the two models were compared below in Table 3.1
in order to ensure that the variance was no greater than ±3dB(A) at any of the assessment
locations.
Table 3.1: Comparison of Predicted Values for LA10(1 hour) at Assessment Locations
Receiver
Location
Reference
NPL
LA10 dB
Predictor
LA10 dB
Difference
dB
R01 78 76 -2
R10 73 73 0
R17 71 72 +1
R19 72 72 0
3.9.4.7 Choice of Receiver Locations
Free-field traffic noise levels have been predicted at twenty-five locations in the vicinity of the
proposed and existing roads.
The (national) coordinates of all locations are provided in Table 3.2. These receiver locations
are illustrated in Figure 8.3 (Noise & Vibration Chapter).
December 2007 Page 27