3.   Risk in Environmental Noise Assessment

3.1  Introduction

An important factor in the consideration of site specific noise modelling is the strong influence of commercial and practical constraints which are more prevalent than in strategic mapping. In these instances, the commissioning party with ultimate responsibility for allocating timescale and budget resources may not be aware of the available choices, nor appreciate the varying risks of different approaches. Given the degree of flexibility and interpretation permitted by relevant assessment criteria that may drive the requirement for predictive studies, industry expectations of what may be involved in conducting a predictive study are understandably wide ranging. These factors will often lead to a situation where the scope of a study will be limited or compromised without proper regard to the consequential trade off in terms of the risk and significance of an incorrect assessment outcome.

In the context set out above, the challenge for practitioners is to raise the end user’s appreciation of the potential decision risk associated with different approaches, and to develop tailored assessment strategies that strike an appropriate balance between the scale of resources required for a predictive study and the costs (social, financial or otherwise) and likelihood of an incorrect decision resulting from a compromised study. To achieve such a balance requires the assessment design to 'begin at the end'; that is, prior to developing an assessment strategy, consider the nature and scale of the decision to be made, and how predicted noise data could be used to inform the decision. In some cases, designing the assessment strategy in this way may lead to a number of possible approaches to conducting predictions, or may ultimately conclude that predictions do not represent a viable decision making tool (requiring either the available resources to be re-considered, or evaluation of alternative methods of informing the decision). This type of approach provides the opportunity to focus inevitably limited resources on the most critical elements of a study that influence the decision for which the assessment is intended to inform.

The above considerations highlight the need for noise predictions to be used in a way that appropriately manages the risk of incorrect assessment outcomes. It is worth emphasising that there are two main risks when considering the implication of an incorrect assessment outcome. The first and perhaps most commonly recognised risk is that of an outcome where a prediction fails to represent the full scale of noise levels that occur in practice, leading to a situation where environmental noise levels breach acceptable levels with associated social and financial consequences. However, the second and perhaps most frequently underestimated risk is that of the unnecessary development costs (direct costs as well as those associated with lost development opportunities) of incorrect assessments arising from a prediction study that overestimates noise levels experienced in practice. The latter risk is an important consideration within the current assessment framework where worst case approaches are frequently relied upon to address the challenges and limitations that apply to practical environmental noise studies.