Conflict in the mitigation process

Processes and links to deliver effective mitigation

(adapted from Lochner 2005)

Terns

Mitigating noise and vibration impacts can be difficult.

Although this blog applies equally to noise and vibration, for brevity I’m going to adopt a common shortcut that is popular amongst acoustics professionals and simply use the term ‘noise’ to refer to both ‘noise’ and ‘vibration’. This article is also set in the context of the UK planning and permitting regimes, though the principles are applicable to others.

As the above process diagram shows, there are typically many steps to delivering effective noise mitigation in the built environment. What is not shown is the inherent conflict between the disciplines, stakeholders and planning processes at each step of the way, which complicate the process greatly.

Conflict arises not just because the physical aspects of noise mitigation tend to require space (which is always at a premium), mass (which is unwanted when striving for lightweight structures) or costly materials/intricate details (never popular with cost consultants or contractors). It starts with the first and most effective action in the noise control hierarchy, which is to reduce or eliminate the source of noise from the project. In many cases, this can only be done early in the pre-application design phase; the further a project progresses along the design process, the harder it becomes to remove or alter the noise source. In an ideal world, as shown in the process diagram, the design process should progress in parallel with the baseline, screening and scoping EIA activities, enabling initial EIA input to influence early iterations of the project design. This is referred to as primary or inherent mitigation, that which is 'baked into' the design of the development at the pre-application stage, and which generally offers the best chance to reduce or avoid impacts. Some good examples of primary mitigation are:

orientating seating in a stadium so that crowd noise is directed away from sensitive receptors
routing an access road to an industrial facility away from residential properties
locating the access corridors on the noisiest facade of a block of flats
arranging dwellings in a horse shoe arrangement around outdoor amenity space, thus protecting it from nearby road noise.

Of course, some inherent mitigation that is desirable for noise may conflict with design codes or operational requirements, or the objectives of other environmental disciplines. This is the point at which acoustic consultants need to be able to quickly and concisely lay out the benefits of providing inherent mitigation, and the ramifications of not providing it. The project team will have a process to make decisions on each issue, which may be collaborative or adversarial, but for the noise mitigation to be taken forward at this stage the acoustic consultant must be an effective advocate. Unfortunately it is unlikely that there will be much in the way of model outputs at this stage, so the consultant will often have to put forward their position on the basis of legal requirements, best practice, sensitivity tests and a good knowledge of what has passed through the planning system in the past (and what hasn’t). This is undoubtedly one area where experience and confidence is tremendously helpful, and a frequent source of anxiety for new consultants.

It can be particularly difficult to demonstrate the need for, or effectiveness of, primary mitigation when the design might yet vary as is frequently the case with DCO parameter plans. In such cases, it must be demonstrated that the mitigation is needed and will be effective whatever the form of the final development takes within the ranges of parameters that may be varied.

External glazing to balconies, which reduces road noise to occupants. It is impossible to know whether this was primary or secondary mitigation just by looking at it.

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Construction Noise