The airspace above and subsoil below a highway often has significant development value (or ransom potential), especially in more densely populated urban areas, where space is at a premium. The increasing popularity of basement development and projects such as Crossrail have highlighted the huge values that this land can command. The extent of statutory highway consents required to develop over or under a highway can also be a contentious question, especially where a local highway authority can see potential to charge fees for licenses and inspections.

In terms of the subsoil, Lord Denning famously described the extent of that which vests in the highway authority as being the "top two spits" (two spade depths) in 1954. Since then much argument has taken place between practitioners as to what that really means. The question has, however, managed to avoid further litigation and, until recently, the Court has not been required to address it. The extent of the airspace above the highway that vests in the authority has, until recently, never been subject to Court scrutiny.

On 5 December 2018 the Supreme Court issued its judgment in the case of London Borough of Southwark and another v Transport for London [2018] UKSC 63. The appeal concerned the interpretation of provisions of a highways transfer order made under the Greater London Authority Act 1999 and by extension, to the meaning of section 265 of the Highways Act 1980, which concerns the transfer of rights, liabilities and property between highways authorities.

The judgment primarily addresses a complicated question of statutory interpretation (to determine how much of the vertical plane of a highway had been transferred between the parties in various different circumstances). To reach a judgment, however, the Court had to address the question of what operational or statutorily vested highway actually means.

The Court described Denning's old 'two top spits' phrase as "colourful" and instead chose to adopt a more helpful phrase of "zone of ordinary use" to describe the vertical extent of the land that is vested in a highway authority for highways purposes.

The Court described this zone as being a flexible concept, differing according to the nature of the highway concerned and capable of change over time if the nature or intensity of public use of a particular highway changes. The zone should include sufficient subsoil and airspace to allow the support, drainage, public use, supervision, repair and maintenance of the highway in question.

For example, on a public bridleway shallow foundations of, say, a metre or so deep and airspace clearance of ten or twelve feet to accommodate a horse and rider may be sufficient and would constitute its zone of ordinary use. In a busy urban street, along which trams run alongside multiple lanes of buses and cars, pedestrians and cyclists, deep foundations may be required to support intensive use, enable complex drainage needs and to house the necessary apparatus for street lighting etc, in addition airspace to accommodate overhead electric lines and double decker buses will be required. Accordingly, the zone of ordinary use will be much wider for this highway (and certainly much deeper than the top two spits, if that phrase is taken literally).

In simple terms, the "zone of ordinary use" of a highway is established by looking at the actual use and construction of that highway and applying a modicum of common sense. It consists of what is necessary (above and below the surface) for the highway to function, for the authority to maintain the way and for the public at large to use it.

Let's see whether this latest definition also stands the test of time and the subject can avoid litigation for the next 60 plus years.

*Please note this article applies to the legal position in England and Wales only

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