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Appendix 2 - Prioritisation Matrix
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.
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:
- Building use (only residential considered at this stage, although other building types may be considered in later phases of development)
- Appropriate strategic noise level at 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 log 10 (number of people annoyed)
Where:
Noise Level at building = L den
Number of people annoyed = (N A x P A x A) / 100
where
N A = Number of address points within building
P A = Population per address
A = % people annoyed
Property 1 Berkeley Street (Adjacent to M8 in Glasgow)
Noise level at building | 80.9dB L den |
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No. of Address Points within building (N A) | 16 |
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Population per Address (P A) | 2.36 |
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% people likely to be annoyed by road traffic noise (A) | 79.7 |
|---|
BPS | 80.9 + (10 x log 10((16 x 2.36 x 79.7)/100)) = 95.7 |
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Property 2 309 Great Western Road, Glasgow
Noise level at building | 72.1 L den |
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No. of Address Points within building (N A) | 6 |
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Population per Address (P A) | 2.36 |
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% people likely to be annoyed by road traffic noise (A) | 52.3 |
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BPS | 72.1 + (10 x log 10((6 x 2.36 x 52.3)/100)) = 80.7 |
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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.
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 L den 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. For n Building Prioritisation Scores the logarithmic sum is given by the follow equation:
- Where x i is the i th Building Prioritisation Score.
- 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 log 10 (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.
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.
Prioritisation Matrix
Source Prioritisation Score Example
The following graphic shows a section of the major road network with buildings that have had their 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) for each road segment. 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.
For Example:
In Figure 1, below, each 100m source segment has a unique ID. For illustrative purposes, each segment has been uniquely coloured. The ID of the nearest source segment to each building is then assigned to each building and, for illustration purposes, each building has been assigned the same colour as its nearest source segment.
Taking road segment 03921 (Brown)as an example, the Source Prioritisation Score for this segment is equal to the logarithmic sum of the BPS scores for all properties for which this segment is the closest ( i.e. all of the brown coloured buildings). These buildings have the following BPS: 83, 86, 86, 88, 89, 92, 92, 91, 84, 76, 75, 78, 78, 78, 75, 72, 75, 74, 72, 71, 71 and, as such, the Source Prioritisation Score is given by:
Please note that in this example integer BPS values have been used. However, when determining SPS values for all source segments BPS values to one decimal place have been used.
Figure 1: Noise Source Segments (With IDs) and Buildings with Associated BPS. The source segments have been uniquely coloured. All buildings have been assigned the ID of the road segment closest to it and then coloured using the same colour as the road segment.
7 Potential Actions
It is important to note that the potential actions listed below are also relevant to the Transportation Action Plan and indeed the potential actions contained in the Transportation Action Plan are equally relevant to this plan.
Consideration should be given to the benefits of replacing the road surface with a low noise surface when the road is next due for resurfacing. Further research should be encouraged into the comparative benefits of different surfaces.
Consideration should be given to the possibility of reducing the number of vehicles / HGVs using this stretch of road.
Consideration should be given to the possibility of reducing the speed limit on this stretch of road.
Consideration should be given to the construction of a barrier along this stretch of road.
Any further construction of noise sensitive developments in this area / along this stretch of road should be afforded protection from noise using a noise reduction technique appropriate to the design.
Consideration should be given to updating the Local Transport Policy to include transport noise and noise reduction as explicit and integral objectives in the design and development of the transport strategy
Consider how the objectives of the Strategic Noise Action Plan can be integrated into Local Plan Policy and relevant supplementary planning guidance..
Consideration should be given to expanding the Scottish Noise Mapping Website to include clear guidance as to when members of the Public affected by noise should contact their Local Authority and when they should contact SEPA in relation to noise from industrial and port areas.
Keep in place the working group so that it can co-ordinate the taking forward of the Action Planning Process.
Air Quality Action Plans should take into account noise e.g. when redirecting traffic.
8 The Noise Model
The following recommendations concern possible improvements to the noise model. Any potential improvements to the model will have to be evaluated in conjunction with the Scottish Governments noise mapping contractors to establish if they are practical, feasible and worthwhile. For example some data requirements can push the limits of available technology and have implications for processing time.
Consideration should be given to how the data used in the model can be improved in ways that will increase the accuracy of the maps in future years. This should be consistent with any developments on noise mapping developed within the EU.
Consideration should be given to improving the data available on road surfaces within the agglomeration in order to improve the accuracy of the model.
Consideration should be given to improving the data available on night time noise in order to give a more accurate L night and therefore L den.
9 Intervention Types
Reduce speed limits
Limit numbers of vehicles
Limit time of day vehicles have access
Restrict certain types of vehicles
Redirect vehicles
Use low noise road surface
Introduce speed control measures e.g. chicanes, narrow roads, road markings, bends, Changing vehicle priority.
Introduce a barrier
Require the use of low noise tyres (national / international support & research needed)
Variable speed limits (related to time of day)
Through EC press for quieter vehicle requirements e.g. exhaust noise limits, quieter tyres, further research into low noise road surface
Consider locating taxi ranks / bus stops away from residential property
Consider location of pedestrian crossings, with due regard to road safety
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