"Corridors" refers to planning controls such that new homes are not permitted within a certain distance of overhead power lines and vice versa.
The UK does not have corridors, on EMF or any other grounds. The only restriction close to a power line is to comply with the safety clearance distances to avoid flashover and with EMF exposure limits (but these normally do not pose any constraint in practice because for all except a very few low-clearance power lines the fields are below the exposure limits even directly underneath them).
The absence of corridors is not just by default or because no-one has thought about it. It is a definite national policy not to have corridors. The issue was analysed by the stakeholder group SAGE in its First Interim Assessment in 2007. Government responded through a Written Ministerial Statement in 2009, rejecting corridors, as they were not judged in the interests of the country to introduce:
"However SAGE's cost benefit analysis does not support the option of creating corridors around power lines on health grounds. The Government therefore considers this additional option to be disproportionate in the light of the evidence base on the potential health risks arising from exposure to ELF/EMF and has no plans to take forward this action." (para 4)
The position before 2009
That 2009 announcement confirmed an approach that had previously been established, among other places, through Parliamentary Questions and Answers. For example, on 20 November 2007, Iain Wright, Undersecretary, DCLG answered a question from Mr Swire MP on building near power lines:
“No planning guidance on this subject has been issued to local authorities. At present, there are no planning restrictions on development close to power lines other than the need to observe safe clearance distances.”
Widths of corridors that have sometimes been suggested
The UK has no restrictions on distances between homes and power lines as explained above. However, people often suggest what they think should be adopted as a minimum distance between homes and power lines. Many different numbers are proposed for that distance. We list here some of the common numbers and give our best understanding of where each one comes from (though of course these origins are only our guesswork, we cannot know for certain what the person using the figure had in mind).
- 60 m was a figure used by SAGE in its First Interim Assessment, derived as the average distance for the magnetic field from 275 kV and 400 kV power lines in England and Wales to fall to 0.4 µT SAGE also gave an equivalent figure of 30 m for 132 kV overhead lines. See more detail below.
- 200 m was an intermediate cutpoint used in the analysis of Draper et al 2005. See more detail below
- 200 m was proposed by a group of MPs in 2007 as an extension of SAGE's 60 m
- 200 m and 400 m are distances used in part of Austria and in relation to specific power lines in Germany as a trigger for placing the line underground, though this is not, as far as we are aware, on EMF grounds
- 300 m has been used several times as the outermost cutpoint in analysing epidemiological studies of power lines
- 500 m is sometimes mentioned but we are not aware of any obvious source for this figure
- 600 m was the furthest cutpoint used in the analysis of Draper et al 2005. See more detail below.
Some of these in more detail...
60 m/30 m
SAGE itself said that, if corridors were introduced, they should be set at the width where, on average, the magnetic field falls to 0.4 µT. This is because 0.4 µT is the field at which it is often said the statistical association between magnetic fields and childhood leukaemia appears. (In fact the true situation is more complicated than this, but 0.4 µT is probably as good a figure as any other to use given all the uncertainties.)
SAGE calculated that this distance is 60 m for 275 kV and 400 kV power lines and 30 m for 132 kV power lines. It used the same data as are presented on this site - see here for how the field typically falls with distance, here for data on a sample of actual lines and the distance for the field to fall to various different values. The distance is measured from the centreline (so 120 m total width, or alternatively about 50 m from the outer conductors, given that the crossarms of 400 kV pylons are nearly 10 m wide).
This is of course only an average - for some lines the field falls to 0.4 µT closer, and for some it extends farther. SAGE calculated that 70% of lines fall to 0.4 µT at or within 60 m, and that just 15% of homes would still have a field greater than 0.4 µT at distances greater than 60 m (See Sage First Interim Assessment, Supporting papers, page 98).
The 200 m figure is usually derived from the Draper study of childhood leukaemia. That study looked at leukaemia rates all the way out to 600 m from the power lines. But for convenience it analysed the variation separately in 100 m bands, and for convenience again, for some analyses it grouped those into just two bands, 0-200 m and 200-600 m. The way the results came out, there was a higher rate in the 0-200 m band and a lower rate in the 200-600 m band. This has led some people (e.g. the Cross-Party Inquiry in 2007) to suggest that corridors should be set at 200 m from the powerline (400 m total width). But whilst the risk in Draper certainly falls with distance, the 200 m figure itself is more based on the fairly arbitrary choice of cutpoints for analysis in the Draper study than on the actual results.
600 m is the farthest distance the original Draper study considered, and as there was still an increased leukaemia rate at this distance, some people have suggested any corridors should be 600 m. The follow-up study looked at larger distances, out to 1000 m, but found that the risk seemed to be confined to the original 600 m.
But 600 m is just the farthest distance Draper originally considered. The choice of 600 m was based on a calculation that the farthest possible distance to get a field of 0.1 µT, the reference category, was 400 m. So 400 m would have been sufficient distance to ensure the study captured every possible instance of fields above 0.1 µT. But the Draper study added a margin of 200 m to be absolutely sure.
We discuss some of the other issues about property and power lines here. See also the situation in the USA where power lines do have "corridors" (known there as "rights of way").
Some other countries have "rights of way" along power lines where homes are not built, though this is not on EMF grounds. Some countries in Europe have EMF limits specific to power lines, though expressed as the field itself rather than as a distance.