significance of construction phase impacts can be determined. The aim is to prevent significant effects at receptors due to the implementation of effective mitigation.
37.
With the implementation of effective mitigation measures, the residual impacts can therefore be considered to be ‘not significant’ in accordance with guidance provided by the IAQM. A matrix is not provided in the guidance to determine significance.
20.4.3.2 Construction Vehicle Exhaust Emissions 38.
Assessment of construction vehicle exhaust emissions was not undertaken for the East Anglia ONE DCO Application, as it was concluded that vehicle movements along construction access routes would not constitute a significant increase in traffic flows. Review of traffic data provided for East Anglia THREE identified road links which will experience a more significant increase in traffic flows as a result of construction vehicles. Assessment of construction vehicle exhaust emissions was therefore required.
39.
The potential impact of exhaust emissions from construction vehicles accessing the onshore electrical transmission works including access, was assessed using the Highways Agency’s Design Manual for Roads and Bridges (DMRB) (Highways Agency 2007). This is a spreadsheet tool which allows for the prediction of air pollutant concentrations at specified distances from road sources, accounting for the background pollutant concentrations (obtained from Defra’s LAQM support portal for the respective year of assessment). The main pollutants of concern for human health as a result of vehicle emissions are annual mean concentrations of NO2 and PM10. Concentrations of these pollutants were therefore the focus of the DMRB assessment.
40.
The DMRB methodology requires data relating to vehicle speeds, the distance between the receptor and the roads carrying the traffic, the proportion of Heavy Goods Vehicles (HGVs) and changes in future exhaust emissions given legislative and technological controls. These data were utilised to predict changes in air quality resulting from the proposed East Anglia THREE project were established and pollutant concentrations compared to the Air Quality Strategy Objectives.
41.
The DMRB methodology states that there is unlikely to be any significant effect on air quality due to changes in road traffic flows at properties beyond 200m from any roads. Therefore information on all major roads within 200m of the selected receptor location is required. Traffic flow data, comprising annual averaged daily traffic (24-hour AADT) flows and traffic composition, including percentage HGVs were used to inform the assessment. Details of the expected traffic volumes are provided in Chapter 27 Traffic and Transport.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 20 Air Quality Page 15
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