1.1.1 The methodology developed for appraising Landscape, Heritage of Historic Resources, Biodiversity and Water Environment is based on a qualitative 'environmental capital' style approach, in contrast to the more quantitative methodologies for noise and air quality. This approach has being developed by the statutory environmental bodies (Countryside Agency, English Nature, English Heritage and the Environment Agency) in co-operation with DfT. The four main elements of the approach are:

to describe sequentially the characteristic environmental features being appraised;
to appraise the environmental capital, using a set of indicators, by assessing:
- the importance of these characteristic features;
- why they are important and to who; and
- their inter-relationships with other environmental attributes;
to describe how proposals impact on the environmental features, including effects on its distinctive quality and substantial local diversity; and
produce an overall assessment score for the Appraisal Summary Table (AST) on a standard textual seven point scale (Slight, Moderate or Large Beneficial or Adverse, plus Neutral).

1.1.2 The methodology developed for townscape is analogous to the environmental capital approach developed for landscape.

1.1.3 The appraisal methodologies for each sub-objective are set out in detail in TAG Unit 3.3.7 to Unit 3.3.11 with accompanying Worksheets provided at the end of the respective TAG Units which should be used to record the appraisal results. The following paragraphs discuss some of the common issues that arise for these sub-objectives, such as: application of the approach to plans and strategies; study type; and the range of available data.

1.2 Application to Plans and Strategies

1.2.1 Appraisal, using this approach, should be possible at any stage in the development of proposals from the general (in this context strategies) to the specific (plans). Ideally, a full dataset, such as that derived from an Environmental Assessment, would be available and a detailed appraisal of the environmental capital and effects on it could be made. However, the approach can be applied using what data is available at any stage; where this is less than fully detailed then the limitations of the data should be identified as part of the appraisal process. Increasing confidence can be placed in the results of appraisal as the level of data improves through the development of proposals. The available detail will depend on the scale of proposals under consideration as well as the stage in development which they have reached. At a local site or plan level, the detail should be substantial and specific, but at a more strategic level data may be either very generalised or too site specific and restrict the appraisal conclusions which can be reached. Guidance on application of this approach to strategic level studies is included for each of the sub-objectives.

1.2.2 This guidance is relevant to road schemes, other modes of transport, and mixed modes. It is also relevant at both the plan (or project) and strategic level of appraisal. For project level appraisal, the mode and route for each option is more likely to be known, though an Environmental Assessment may not be available for all options. The appraisal process is made more complex if there are many different potential nodes with different potential routes and modes of connection. Such circumstances are especially likely for strategic level studies and may also be applicable to area or corridor studies. Specific guidance on appraisal in such circumstances is provided below.

1.3 Study types

1.3.1 It is important that the appraisal process includes consideration of all relevant transport options. For multi-modal studies, these could include some or all of the following:

do nothing;
do minimum;
the transport operators' preferred schemes;
the best practical environmental option still meeting transport objectives;
demand management alternative;
combination of modes; and
packages of measures.

1.3.2 A distinction is made between studies that utilise route data, and those that look at gross traffic movements within areas in a study region. Plan studies utilise route based information, whilst strategy studies usually, but not necessarily, rely on area based data. Corridor studies can fit into either category depending on their breadth and the way in which data has been collated. The methodologies for each study type are broadly similar in the way they characterise the environment. The main difference lies in the impact details available, and therefore the accuracy of impact significance estimates. The methodology to be employed for any given study should be obvious from the data produced during the assessment process.

1.4 Available Data

1.4.1 It is recognised that the approach at each level is likely to be constrained by the availability of data on the details of the proposals and on the baseline environment (and therefore the potential impacts). The methodologies attempt to be as flexible as possible, theoretically being applicable with varying amounts of data. However studies for both strategies and plans will utilise the same baseline datasets. The amount of detail regarding the environmental capital in a study area is not determined by the strategic scale that the proposal operates at, but rather by its geographic scale. Data on many environmental features will be available and can be used to help indicate importance at virtually any geographic scale. However, for large study areas the other more qualitative aspects of importance will not be discernible, affecting the completeness of the environmental capital appraisal. In many, but not all, cases the geographic and strategic scales will be linked and it is likely that the larger proposal scales will also be more strategic.

1.4.2 The main difference between studies based on route and area data will be the availability of data on potential impacts. Area studies cannot provide accurate data on the impacts because the effects at the route level are not known. The detail of a study based on area data will also be limited by the size of the area units used. For some strategy studies, these may be quite large (several km²) and therefore the impact data is likely to be coarse in comparison with route studies.

1.4.3 The level of detail and confidence achievable by the appraisal will vary according to the scale of the proposals and their stage of development. Where data on the local environment or the potential impacts of the proposal are unavailable, or highly uncertain, then assumptions will need to be made. Sensitivity testing should be encouraged, with any assumptions clearly stated and, where appropriate, the precautionary principle applied.

1.5 Accumulating Site or Location Specific Results

1.5.1 The text in the preceding sections in this TAG Unit, and in the related TAG Unit 3.3.7 to Unit 3.3.11, has been taken from the original version of the Guidance on the Methodology for Multi-Modal Studies as published in March 2000. A Supplement has been issued subsequently which clarifies the approach to be adopted for the accumulation of site or location specific impacts on landscape, townscape, heritage, biodiversity and the water environment in circumstances where a number of key environmental resources are affected by an option (‘Key environmental resources’ is the term used to describe those components of the natural and human world that provide qualities and functions which are considered by the community (local, regional, national or international) to be of particular value.). This supplementary guidance was discussed and agreed with the environmental statutory bodies (Countryside Agency, English Nature, English Heritage and the Environment Agency) and is included in the remainder of this section.

1.5.2 The advice in TAG Unit 3.3.7 to Unit 3.3.11 on the accumulation of environmental impacts is variable across the five sub-criteria. The advice given in the supplement is based on that given for biodiversity and the water environment. It is intended to provide a systematic basis for accumulating site or location specific results, while also allowing for the exercise of expert judgement.

1.5.3 Many multi-modal studies will affect quite large geographical areas. Inevitably, key environmental resources will vary across these large study areas. For example:

there may be areas of archaeological importance in one part of the study area, and historic buildings in another;
woodland may be a key biodiversity feature in one location, with wetland being key elsewhere;
there may be several towns or cities in a study area, each with different townscape characteristics.

1.5.4 Further variation is likely to arise because the nature of options (and hence their impact) may vary across the study area. For example, one part of the study area may be affected by proposals for a guided busway, while a road scheme may be proposed elsewhere.

1.5.5 These variations may be addressed by treating each key environmental resource separately. Key environmental resources should be identified on the basis of the coherence of character within each resource and the distinctiveness of character between resources. It is likely that the geographical scale of the resources will vary between impact types. For example, key landscape resources will often be large geographic areas, while key biodiversity resources may be quite small. Excessive detail should be avoided - the level of detail should be no more than is needed for robust decisions to be taken.

1.5.6 Identifying key environmental resources in this way enables the nature of the resource to be concisely described using the environmental capital approach. It also allows the impact of that element of the option relevant to the resource to be clearly stated. Together, these allow the significance of the impact on each resource to be assessed relatively easily, using the guidance provided in TAG Unit 3.3.7 to Unit 3.3.11. The results of this process should be an assessment on the standard seven point scale for each key environmental resource.

1.5.7 These separate assessments must be combined to prove an overall assessment for the option as a whole, suitable for use in the Appraisal Summary Table (AST) - see TAG Unit 2.7.2. The procedure to be adopted for this is discussed below. It is intended to provide a transparent and systematic basis for accumulating results, while also allowing for the exercise of expert judgement.

1.5.8 The following guidelines should be used to derive the overall assessment score for an option from separate assessments of impact on a number of separate key environmental resources:

Most adverse category. The principle here is that an option as a whole should be assessed according to the most adverse assessment of the resources affected. For example, if an option affects, say, five resources, of which one is in the 'large adverse' category and the remaining four are 'slight adverse', then the overall assessment score should be 'large adverse'. The rationale for this approach is that highly adverse impacts should not be diluted or masked by less adverse impacts. It also encourages the development of alternative options which avoid such adverse outcomes.
Cumulative adverse effects. The principle here is that, where it is clear that there is a cumulative effect across a range of resources, then the option as a whole should be scored in a higher category than the resources in isolation. For example, a proposal may affect a number of resources, each of which is assessed 'slight adverse'. Where it is clear that there is a cumulative effect across the resources, the option as a whole would be assessed as 'moderate adverse'. The existence of cumulative effects will usually depend on there being some similarity in the characteristic features or attributes of the affected resources. For example, a group of biodiversity sites might all be habitats for the same species of plant or animal.
Balancing adverse and beneficial effects. The principle here is that, where there is a genuine compensatory effect, adverse impacts on some resources may be balanced by beneficial impacts on others. The key issue is whether there are genuine compensatory effects. In most cases, it will be necessary to consider the impacts on each resource at a detailed level, to ensure that the features lost from one resources are provided at another. For example, adverse impacts on groundwater supply at one location would probably need to be offset by beneficial impacts on groundwater supply at another location - beneficial impacts on floodplain would probably not provide genuine compensation. The scope for genuine compensatory effects will often be determined by the substitutability of attributes. In most cases, there is great uncertainty about the scope for substitutability, thus balancing should err on the side of caution. In particular, balancing should be restricted to 'slight' or, exceptionally, 'moderate' impacts. It is very unlikely that adequate compensatory effects can be identified to justify any balancing of 'large adverse' or 'very large adverse' impacts.

1.5.9 Clearly, these guidelines require an understanding of the key environmental resources and the impacts of the option on them. In addition, judgement and expertise are required to apply them satisfactorily.

1.5.10 Good reporting is a key factor in ensuring that assessments are transparent and acceptable to steering groups and stakeholders. Reporting should include the following:

the assessment of impact for each key environmental resource should be clearly summarised, distinguishing between the characteristics of the resource and the nature of the impact on the resource;
a summary list of resources and their specific assessments should be provided;
a statement should be provided, explaining how the overall assessment has been derived from the resource specific assessments and giving particular emphasis to the reasons for any cumulative adverse and balancing effects adopted; and
in addition to the overall assessment and a qualitative comment, the Appraisal Summary Table should provide (in the quantitative column) a summary of the numbers of key environmental resources in each scoring category.

2. Further Information

The following documents provide information that follows on directly from the key topics covered in this TAG Unit.

For information on:

See:

TAG Unit number:

Appraisal Summary Table

Transport Appraisal and the New Green Book

The Appraisal Process

TAG Unit 2.7

TAG Unit 2.5

3. References

DETR (2000). Guidance on the Methodology for Multi-Modal Studies

DfT (2002). GOMMMS Supplement 1

4. Document Provenance

This Transport Analysis Guidance (TAG) Unit is based on Chapters 4, Section 6 of Guidance on the Methodology for Multi-Modal Studies Volume 2 (DETR, 2000) plus GOMMMS Supplement 1 (DfT, 2002).

Technical queries and comments on this TAG Unit should be referred to:

Integrated Transport Economic Appraisal (ITEA) Division
Department for Transport
Zone 3/08 Great Minster House
33 Horseferry Road
London
SW1P 4DR
itea@dft.gsi.gov.uk
Tel 020 7944 6176
Fax 020 7944 2198

Updated: April 2009

Documents

Guidance documents - Expert

3.3: The Environment Objective

TAG unit 3.3.6: The Environment Capital Approach

WebTAG

Department for Transport

Transport agencies

Transport bodies

UK Government

Key