Noise mapping Ireland’s national road network
27 June 2013
Author: Dr Eoin King MIOA MIEI, acoustics engineer, Roughan & O’Donovan
Noise pollution has become a critical issue in the assessment of transportation systems. Excessive exposure to environmental noise may induce annoyance, sleep disturbance, hearing impairment and cardiovascular disease and can also impair the cognitive development of children.
The World Health Organization (WHO) has estimated that at least one million healthy life years are lost every year from traffic-related noise in western Europe, while the social costs of noise from road and rail across the EU have been valued at €40 billion a year.
To address the situation, in 2002, the EU released the Environmental Noise Directive (END), which established a framework for environmental noise assessments. The END sets out a cyclical process where strategic noise maps and noise action plans must be developed by Member States every five years for major cities, roads, railways and airports.
In Ireland, S.I. No. 140 of 2006 (the ‘Environmental Noise Regulations’) transposed the END into national legislation. These regulations designate the National Roads Authority (NRA) as the body responsible for the development of noise maps for all national major roads. A strategic noise map is a graphical representation of environmental noise in an area and includes an assessment of population exposure within that area.
Noise map results then form the basis of noise action plans, which have the twin aims of protecting areas that have been identified as having a positive noise environment and improving areas where noise exposure is deemed excessive.
PHASES OF NOISE MAPPING
The first phase of noise mapping was completed in June 2007. This involved the preparation of noise maps across Europe for all cities with more than 250,000 inhabitants, major roads (with more than six million vehicle passages a year), major railways (with more than 60,000 train passages a year) and major airports (with more than 50,000 movements a year).
In Ireland, noise maps were developed for the city of Dublin, along with approximately 600km of major roads and described the exposure of about 1.25 million people, the majority of which were in Dublin. The first phase of noise mapping was dealt with by five noise-mapping bodies, while 26 action-planning authorities were involved in the development of the associated action plans.
The second phase of noise mapping, in June 2012, saw a reduction in the thresholds for cities, major roads and major railways that were required to be mapped. This significantly increased the extent of mapping requirements for relevant authorities.
In the case of major roads, the threshold dropped from six million to three million vehicles per year – an annual average daily traffic of approximately 8,200. Thus, the length of major roads required to be mapped in Ireland increased from approximately 600km to over 4,000km, resulting in the largest environmental noise assessment study undertaken in Ireland to date.
The second phase required a number of non-national major roads, which were also deemed to be carrying in excess of three million vehicles per year, to be mapped. Under the regulations, the local authorities within whose jurisdiction these non-national roads were located were responsible for the preparation of these noise maps.
It soon became apparent that a centralised approach to noise mapping major roads (outside the cities of Dublin and Cork) would be the most efficient means of meeting Ireland’s statutory obligations and, in January 2012, such an approach was adopted. Thus, the NRA developed strategic noise maps for all major roads outside agglomerations, encompassing both national and non-national roads.
The non-national roads were mapped by the NRA on behalf of the various local authorities who provided ‘model-ready’ data to the NRA for inclusion in the noise modelling calculation. All local authorities with responsibility for mapping major roads in their jurisdiction participated in this centralised approach, which totalled 29 local authorities. In total, approximately 3,600km of national roads and 650km of non-national roads were required to be mapped (see Figure 1).
Before any calculations were performed, it was important to establish a national unified approach to noise mapping. The regulations designate the Environmental Protection Agency (EPA) as the lead authority responsible for the supervision and guidance of the various noise-mapping bodies and to ensure a consistent methodology in developing strategic noise maps was adopted across Ireland.
The EPA established a National Steering Group, consisting of all major stakeholders to achieve this, including members from the Department of the Environment, the NRA, Dublin City Council, Cork City Council, the EPA as well as Irish Rail, the Rail Procurement Agency and some local authorities. The purpose of the Steering Group was to co-ordinate key activities, ensure timely compliance with the END and to provide a platform to share experience and knowledge.
A National Technical Group was also established to complement the Steering Group. While the Steering Group focused on the overall implementation activities, the Technical Group provided an opportunity to discuss technical issues related to noise map calculations. The NRA Noise Mapping team also met with representatives from Northern Ireland Roads Service to ensure cross border co-operation in developing noise maps in the border region.
DEVELOPING THE NOISE MODELS
The preparation of a noise map is a particularly complex problem and involves the accurate representation of the source of the noise (the road) and the factors that will influence noise propagation away from the source (such as topography, the presence of noise barriers or buildings).Considering the extent of the roads that were required to be mapped this involved the collection and collation of a large amount of datasets. The following were utilised:
Source Model Datasets
- NRA Traffic Model – the NRA maintains a National Transport Model to support transport investment decisions, and facilitate good forecasts of traffic volumes on the road network for different future years and economic conditions. The National Transport Model provides a comprehensive representation of base demand on the transport network, in addition to a series of future year transport forecasts. The Traffic Model was used to determine traffic quantities and composition.
- Roads Database – the NRA’s Roads Database is a GIS repository that contains information associated with the national road network such as carriageway types, road widths, noise barriers, surface types, texture depths and speed limits.
- Ordnance Survey of Ireland – building geometries were extracted from large-scale Ordnance Survey digital mapping. This dataset was then converted to a polygon dataset and attributed with height data and associated population data from Census 2011.
Propagation Model Datasets
- Aerial LiDAR – in 2009, the NRA issued a tender for an aerial LiDAR survey of approximately 3,000km of the national road network to a survey corridor width of 1200m. The survey was completed in early 2011 and outputs included one-metre contours for the entire survey area, building height information for buildings within the survey corridor and a digital terrain model (Figure 2).
- Corine Database – the European Environment Agency’s (EEA) CORINE Land Cover 2000 dataset is a European-wide vector land parcel product derived from satellite imagery R2V processing. The CORINE dataset was developed in the framework of the CORINE programme to establish a computerised inventory on land cover. The dataset was used for preparing a range of policies including environmental, regional development and agriculture policies. For noise calculation, the dataset can be used to provide information on the land cover distribution.
Population Exposure Datasets
- Ordnance Survey of Ireland (OSI) – OSI maintains a wide range of mapping products that are available for use within strategic noise mapping. These included county, electoral district and townland boundaries.
- GeoDirectory – the GeoDirectory data products are developed by OSI and An Post to provide a single point location object for each building in Ireland. The GeoDirectory dataset provides the definitive address database for the country and is an essential component in calculating the population exposed to the various noise bands, information that is required to be submitted to the EU as part of this work.
- Central Statistics Office (CSO) – the CSO publishes statistical information on population based upon Census returns. The most recent Census was held on 10 April 2011, and some of this information is now publically available. The information available on population is issued according to various political boundaries.
Environmental impact assessments for roads in Ireland are generally undertaken using the UK national calculation method, ‘Calculation of Road Traffic Noise’ (CRTN). Thus the EPA instructed all noise-mapping bodies (including the NRA) to develop strategic noise maps using the CRTN method.
Noise calculations were performed on a county-by-county basis, resulting in a total of 26 individual models. Noise-contour maps were developed by calculating the noise level over a grid of receivers spreading from 1000m either side of the road. This was computationally intensive and required calculations to be divided into tiles and run separately on a dedicated computer.
Noise maps also require the determination of the approximate number of people living in dwellings exposed to various noise levels. In order to ascertain these estimates, the noise level at each facade of every building was also calculated. In order to determine the level of exposure, population statistics were obtained from Census 2011 and the ‘small areas’ geographies (areas of between 50 and 200 dwellings) were used.
By combining all the datasets with results from the noise model, it was possible to estimate the average number of people for each residence in the test area (the small area) and assign a noise level to that residence. These estimates were collated to derive an overall exposure level for each county.
All results were successfully delivered to the EPA and each local authority in 2012. Local authorities have now the responsibility for developing noise action plans based on the results of these strategic noise maps. These plans are due to be complete by mid 2013.
All results are also available for public perusal and noise maps are now available for download on the NRA’s website, as well as an interactive noise map displaying results on a national scale (www.nra.ie/Environment/NoiseMaps/). Figure 3 shows a screenshot of the interactive viewer.
The noise maps show a representation of the average environmental noise levels over one complete year. It should be noted that noise maps are primarily used as a strategic tool for large scale planning or policy matters and are not suitable for local noise assessments – more detailed local noise assessments would be required for this.
Finally, Table 1 presents a summary of the national noise exposure estimates for all major roads (both national and non-national) outside the agglomerations of Dublin and Cork.
|National Exposure Results – Major Roads|
|Lden dB(A)||EstimatedPopulation Exposed||Lnight dB(A)||EstimatedPopulation Exposed|
|55 to 59||113,583||50 to 54||75,822|
|60 to 64||68,744||55 to 59||62,981|
|65 to 69||55,888||60 to 64||24,795|
|70 to 74||19,752||65 to 69||849|
Table 1: National exposure results for major roads outside the agglomerations of Dublin and Cork.
Dr Eoin King is an acoustics engineer with Roughan & O’Donovan. He has significant experience in the field of environmental acoustics, having developed many of the largest and most complex noise maps prepared in Ireland to date on behalf of the National Roads Authority. He is a member of the CNOSSOS-EU Technical Forum of Experts, a European working group developing a harmonised European method for noise mapping. In 2009, Dr King became the Irish course co-ordinator for the Institute of Acoustics’ distance learning diploma in Acoustics and Noise Control.
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