The different corridors considered for the proposed new overhead line, potential interconnections between those corridors and our emerging preference, are explained in the CPRSS.

The steps taken to assess corridor options, to identify an emerging preference and first thoughts about where a new overhead line could be potentially be located within an emerging preferred corridor, involve:

The steps taken during this process are described below:

1. Define the study area

For each section of our route, we defined a study area informed by factors including:

• the connection end points identified in the Strategic Proposal;
• the location of large towns and other built-up areas;
• the location of physical features such as estuaries, or protected sites like Areas of Outstanding Natural Beauty, National Parks or nature conservation areas; and
• opportunities to utilise established electricity transmission corridors.

2. Constraint mapping

We then mapped out key features in the landscape that we want to avoid or minimise contact with. These have been informed by planning policy and our professional judgement. These include the built-up areas where people live and other features that may be sensitive in terms of ecology, heritage or landscape, as well as features that may represent planning or technical constraints. The full list is in the CPRSS.

3. Option identification, appraisal and selection

Considering the constraints and opportunities available, using a combination of computer modelling and expert professional judgement, we devise and refine various routes from one connection end to another. These seek to represent different high-level options for making the connection avoiding the identified constraints, for example, routeing on one side of a town or the other.

We then carry out an appraisal of each option with engineers, environmental experts, town planners and other specialists using their professional judgement to consider the implications of each option. This allows us to compare between options on a consistent basis, on topics which are likely to influence the decision. Through this appraisal, we may also identify further options or combinations and do further assessment if needed.

We then consider the relative merits of each option to reach our balanced conclusion on a preferred corridor. The decision is informed by National Grid’s statutory duties, the options appraisal and planning policy - including the Holford and Horlock Rules.

Developing a graduated swathe

Following the selection of an emerging preferred corridor, we produce a graduated swathe which indicates where the overhead line alignment could be routed. This shaded area is darker where an alignment is more likely, when considering environmental factors and identified constraints, and is lighter where it is less likely. This swathe remains indicative until more detailed assessment work is done.