Environmental impacts may be classified in several ways. Normally this would be by topic and by the nature of the impact. It is also possible to classify impacts as large scale (regional, national or even global) or local. Effects upon global and national issues and objectives are difficult to assess by using conventional EIA techniques at individual project level, but at a strategic level the use of more qualitative assessment techniques may be more appropriate; however, hard data may be available to make detailed quantitative predictions and can be particularly useful where an option's effects are uncertain, close to a threshold, or cumulative. But quantification is not always practicable, and broad-based and qualitative predictions can be equally valid and appropriate.
The list below illustrates different scales of geographical impact, though it should be noted that some effects often apply at several different levels - for example, air quality can be an issue at all levels:
For each topic, the area to be considered will have to be defined. The extent of this area will depend on a number of factors, including:
The key areas of environmental effects to be considered in the appraisal of transport options include:
In general, these will apply to all transport options, though it is the role of the scoping exercise undertaken at Part 1 to identify their relevance to a particular option and to identify whether fewer or additional topics need to be covered. For example, a transport option to construct harbours or jetties or crossings of coastal inlets would be likely to require an assessment of impact on coastal processes, including changes to tidal activity, sedimentation and geomorphology as well as the impact on marine ecosystems. On the other hand, land take issues may be less important when STAG is being undertaken on a policy, plan or programme.
Note that for options requiring a SEA, the topics addressed must meet the statutory requirements set out in SEA legislation.
Each sub-criterion may have a number of characteristics. For example, under the water quality sub-criterion, one might have to consider chemical and biological water quality. Each characteristic will then have one or more criteria that can be assigned to it for measuring the effects of transport options. A criterion may be defined as a measurable quantity or quality and is usually related to an objective. For example, if one of the planning objectives is to protect existing woodlands, then a criterion might be used which measures the scale of woodland loss. At the project level this could be related to actual land take, whereas for a policy, plan or programme the criterion might need to be stated in terms of the overall quality of the woodland resource which may be affected. The key criteria and the measured effect upon them are to be reported and summarised in the AST.
Methods for predicting environmental effects and their magnitude are specific to the individual environmental topic and are a matter for expert consultants. For some topics, such as the assessment of impact on landscape character, qualitative techniques will be most appropriate. In other cases, such as the dispersion of emissions, the use of quantitative techniques will be possible. The use of quantitative techniques may offer a greater degree of consistency, but are not always available or appropriate. It is recognised however, that at the strategic level, qualitative techniques will be more appropriate because, for example, options will lack physical definition. Where qualitative techniques are used, the basis of terms employed must be explained and categorisations applied consistently. Numerical scoring or weighting of qualitative indicators should be avoided as it is inaccurate and misleading.
In considering the nature of impacts, the assessment will need to consider whether each is:
The effects may relate to the construction phase, to the permanent physical changes resulting from the development, or to and from the presence of the option once implemented. In relation to plans, impacts may occur in advance of the project construction e.g. blight. The assessment of effects should be made assuming that stated mitigation measures (see Section 7.2.3) are in place, if appropriate.
Climate, pollution and energy effects are normally deduced from traffic forecasts and measurements, whilst most remaining sub-criteria are impacted by physical modification of the environment (e.g. land take).
Environmental assessments of road options have considered the impacts of the option during construction and at year 1 and year 15 after construction. Year 15 is normally taken as the assessment year and the effects of the do-minimum and do-something scenarios are compared for that year. With the emphasis moving towards other modes of transport and strategic studies, it may not be appropriate to adopt such a rigid approach to operational impacts. Rather the assessors should consider:
The level of accuracy of predicted impacts will reduce (and uncertainties increase) as the assessment looks further into the future. It will seldom be appropriate to consider impacts more than 20 years hence. Whichever year is adopted as the assessment year, it must be clearly stated and used consistently when assessing effects across the range of topic areas.
The guidance on the assessment of particular topics set out in later sections is intended to direct the reader to source material from which appropriate techniques may be selected, rather than to specify particular techniques in detail. This is because the selection of technique will need to take into account the nature of the plan, programme or project being assessed and the level of detail available for assessment purposes, particularly on the nature of outputs from any transport model which may be employed.
