Transportation: noise action plan

5 Prioritisation Matrix - BPS and SPS

From initial analysis of the noise maps, the prioritisation process is a method of determining [the provisional assignment of] 'Candidate Noise Management Areas' ( CNMAs) and thereafter 'Noise Management Areas' ( NMAs). Figure 2 outlines the step-by-step journey of the prioritisation process. As noted in Section 2.2, the noise contour maps alone are not sufficient to determine where noise management is required.

Figure 2 - Step by step stages of the Prioritisation Process. BPS = Building Prioritisation Score; SPS = Source Prioritisation Score (see below for more detail).

A prioritisation matrix is generated from a computer based model, where each building is assigned a Building Prioritisation Score ( BPS), which takes into account the predicted road and rail noise levels, in conjunction with the number of people potentially affected and the annoyance response of that exposed population relative to the transportation noise source in question. A Source Prioritisation Score ( SPS) is then determined by first segmenting the road or rail corridors into 100m sections. Each road/rail segment is then given a unique ID and 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 to give the Source Prioritisation Score for that road/rail segment.

All SPS values are prioritised, where the top 1% of SPSs (normally distributed) corresponded to the mean SPS plus two standard deviations to identify the highest three 1% bands of the SPS scores across the road and railway network. These are subsequently referred to as Candidate Noise Management Areas ( CNMAs). Determination of a CNMA is simply a means of highlighting that a geographical area should be considered further in terms of a potential need for noise management. It may be that following further analysis, the area will be disregarded entirely or extended or reduced. Ultimately, the decision about whether or not a CNMA is eventually assigned full Noise Management Area ( NMA) status is dependent on a series of steps during which various assessments and considerations are taken into account. These are outlined in separate Technical Guidance ^[17] .