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Appendix 2 - The Prioritisation Matrix
1 Purpose
The purpose of the prioritisation matrix is to evaluate strategic noise levels within the first round noise maps in terms of the road, rail and air noise sources most likely to cause annoyance to people potentially affected. The prioritisation will enable appropriate actions, required to be determined, based on a consideration of noise levels, the number of people potentially affected and the annoyance response to the noise source.
It is important, in broad terms, to ensure the developed methodology can be used consistently for all three action planning working groups (Edinburgh, Glasgow, and Transportation). It is also, however, important to bear in mind organisational needs and responsibilities.
The matrix must be straightforward, transparent, and consistent. Although the matrix will provide a strategic focus for action planning, a check on the strategic noise levels, all matrix input data and any proposed interventions, will be required prior to the implementation of any suggested actions. In this regard, the matrix will be subject to regular review during the Action Plan process.
The prioritisation matrix, and the related graphics, will be based on Building and Noise Source evaluations as described below. The Source Prioritisation Score being derived from the Building Prioritisation Score.
2 Building Prioritisation Score ( BPS)
The Building Prioritisation Score ( BPS) is an individual value assigned to each building. The input factors for the BPS are as follows:
- Determine Building Use (only residential considered at this stage, although other building types may be considered in later phases of development)
- Appropriate strategic noise level for the building (for the particular noise metric being assessed).
- The number of properties within each building 1
- The population density 2
- The Annoyance response 3
The BPS for each building is then calculated as follows:
BPS = (Noise level at building + 10 x log10 (number of properties within the building footprint x population per building x the percentage of people annoyed by the particular noise source)
Property 1 Berkeley Street (Adjacent to M8 in Glasgow)
Noise level at building | 80.9dB L den |
No. of Address Points within building footprint | 16 |
% people likely to be annoyed by road traffic noise | 79.7 |
BPS | 80.9 + (10 x log10(16 x 2.36 x 79.7)) = 115.6 |
Property 2 309 Great Western Road, Glasgow
Noise level at building | 72.1 L den |
No. of Address Points within building footprint | 6 |
% people likely to be annoyed by road traffic noise | 52.3 |
BPS | 72.1 + (10 x log10(6 x 2.36 x 52.3)) = 100.7 |
3 BPS Maps
To facilitate an understanding of the distribution of BPS values for a particular noise source these have been represented visually in map format. The BPS maps were prepared by assigning each building a score as calculated above. The resultant scores were then divided into 5 point bands, each represented by a different coloured circle. The diameter of each circle is a function of the BPS (the bigger the coloured circle the greater the BPS). The resultant mapped pattern of coloured circles provides a visual representation of where the greatest noise annoyance is likely to occur. As part of the action planning process the maps can, if required, be cross referenced with received noise complaints for particular noise sources. In this way the maps can, if required, be developed for future action planning.
It should be noted that the BPS is an absolute value, and individual properties in Glasgow, Edinburgh, and elsewhere can be directly compared. The colours used in the BPS maps are also absolute, and identify the same BPS values in all areas.
4 Source Prioritisation Score ( SPS) for Roads and Rail
Once the BPS is calculated for each building the Source Prioritisation Score ( SPS), for sections of source line, is calculated as follows.
- Firstly the road network is rationalised so that there is a single centreline to represent motorways, and dual carriageways. Previously these were represented by two separate lines representing opposing carriageways. In addition, junctions are simplified in a similar manner. Similarly, the rail network is reduced to a series of single centrelines that represent railway lines that consist of multiple tracks.
- Road and rail source lines are split into 100m sections (some will necessarily be less than 100m, and these sections have a weighting applied to compensate for the decreased segment length. These shorter sections, in general, occur at junctions and the ends of road/rail sections).
- Each road/rail segment is then given a unique ID.
- For each building with a noise level greater than or equal to Lden 55dB the ID of the road/rail segment that is closest to it is assigned to that building.
- The logarithmic sum of BPS values for all buildings with the same nearest road/rail segment ID is then assigned to the relevant road segment.
- Since some segments are shorter than 100m, a weighting has been applied to each segment that has a length between 50m and 100m. The following weighting was applied, SPS x 10 x log10 (100 รท(segment length)). Hence the maximum correction is 3 and, basically, assumes that if the section was in fact 100m long the distribution of buildings and BPS values would remain constant along the additional length. For lengths less than 50m the correction is not applied due to the large error in summed BPS for such short lengths.. However, since these shorter lengths occur at road ends, lengths of less than 50m are deemed insignificant. Furthermore, in general, they represent less than 0.5% of all source segments. For example, there are 12664 major road sections of which 51 are less than 50m in length. The total length of major roads is approx 1,267km of which the sections with lengths less than 50m sum to approximately 1.5km.
An example of the SPS calculation methodology is presented in Section 7 of this Appendix.
Once calculated, the road and rail network with assigned SPS values are ranked into four categories, based on each section's SPS. To initiate the prioritisation process for each noise source the initial categorisation used is as follows: 1%, 1%, 1%, 97%, from highest to lowest.
5 Airport SPS Maps
The airport source prioritisation maps are based on areas rather then line segments (road and rail). The area SPS values are determined by the logarithmic summation of the building prioritisation scores for all residential buildings that lie within postcode area boundaries. The airport area SPS values are then categorised into four bands as follows: 1%, 1% 1%, 97%. If deemed necessary, the size of the top three airport area SPS bands can be increased.
6 Prioritisation Matrix
7 Source Prioritisation Score Example
The following graphic shows a section of the major road network with buildings that have Building Prioritisation Scores ( BPS) determined. Each of the road sections shown in the graphic equates to a 100 metre lrngth of the major road network, each with a unique ID. In the graphic the road section ID is shown (03919 to 03922). Each line segment and their nearest buildings have been uniquely coloured.
The sequence of events for determining SPS values for segments of source line is as follows.
- Segment line source into 100m lengths.
- Assign Unique ID to each line source segment.
- Assign to each building the ID of the nearest source line segment.
- Logarithmically sum all the building prioritisation scores that have the same unique source segment ID.
- Each unique line source segment is then assigned the logarithmically summed BPS for that particular segment.
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