Visibility splays onto a rural lane

Rural access visibility splay requirements are derived from the speed traffic actually travels on the lane, not from the speed limit painted on the map. Most unclassified rural roads carry the national speed limit of 60 mph, and almost none of them are driven at it. So the first thing a highway authority will ask for on a new or improved field access is a speed survey, and the splay you have to provide follows from the eighty-fifth percentile wet weather speed that survey records.

Get the survey done before you draw the access. Designing to 60 mph produces a splay nobody can deliver, and designing to a guess produces a holding objection from the highway authority that costs you a determination period.

How visibility requirements are derived

A visibility splay is a triangle of land that has to be kept clear so a driver emerging from the access can see approaching traffic, and be seen.

It has two dimensions. The X distance is the set-back of the driver's eye from the edge of the carriageway, commonly 2.4 metres for a residential or light-use access, reduced to 2 metres in constrained situations where the authority accepts it. The Y distance is measured along the carriageway in each direction and is taken from the stopping sight distance for the design speed.

Stopping sight distance combines the distance a vehicle covers while the driver reacts and the distance it covers while braking. The published figures in the national street design guidance run from a little over 20 metres at low speeds to 43 metres at 30 mph and substantially further above that. Take the figure from the highway authority's own design guide rather than from a table you found, because authorities apply the national guidance with local variations and the variation is what gets applied to your application.

The guidance is explicit that measured speeds should be used in preference to the speed limit where the two differ. On a single-track lane with hedges to the carriageway edge and bends every hundred metres, that difference is the whole argument.

Measuring the splay correctly

Three conventions decide whether your drawing is accepted.

The Y distance is measured to the nearside edge of the carriageway rather than to the centre line, which produces a tighter and more realistic envelope on a narrow lane. Draw it that way and annotate the drawing to say so.

Eye height and object height are stated, not assumed. The street design guidance works to a driver eye height of 1.05 metres and an object height of 0.6 metres, which means the visibility envelope is a three-dimensional wedge and anything above 0.6 metres inside it is an obstruction. On a lane with a raised bank or a ditch, the vertical geometry can defeat a splay that looks fine in plan.

The splay is measured from where the driver will actually stop, which on an access with a gate set back is the gate line rather than the carriageway edge. Show the gate, show the stopping position, and dimension both.

Submit the splay on its own drawing, at a stated scale, with X and Y dimensioned, eye and object heights annotated, the obstructions shown, and the land ownership boundaries overlaid.

Speed surveys where the limit is not the issue

A speed survey for this purpose is normally an automatic traffic count over seven consecutive days in a neutral period, positioned where it records free-flowing traffic rather than vehicles slowing for a bend you happen to be beside.

Neutral period means avoiding school holidays, August, the weeks around Christmas and any period when a diversion is routing traffic along the lane. Authorities reject surveys taken in August routinely.

The output you need is the eighty-fifth percentile speed in each direction, with a wet weather adjustment where the authority requires one. Present both directions separately, because a lane often has a faster approach on one side and the splay requirement differs accordingly.

Where the survey shows speeds well below the limit, say so plainly and apply the resulting figure. Where it shows speeds at or above the limit, you have a harder scheme and you need to know that before you spend money on anything else.

Land control over the splay area

This is where rural accesses fail. The splay on a lane with hedges on both sides almost always extends over land you do not own, and often over the highway verge.

Three possibilities, and you need to establish which applies:

1. The splay falls within the public highway. Verges are frequently highway maintainable at public expense, and the highway boundary is rarely where the hedge is. Ask the highway authority for its highway extent records rather than assuming.
2. The splay falls over a neighbour's land. You need their agreement, in a form that binds their successors, or the splay cannot be shown as deliverable.
3. The splay falls over land you own but will sell. Retain it, or reserve a covenant over it, because a splay that disappears on the first plot sale is a condition you cannot comply with.

Where the land is a third party's and they will not deal, a negatively worded condition requiring the splay before the access is brought into use is the usual mechanism, and its viability depends on there being a reasonable prospect of the agreement being reached.

Hedgerow and tree removal consequences

Achieving the splay normally means cutting back or removing hedgerow, and that has three separate consequences.

Hedgerow removal is controlled under the Hedgerows Regulations 1997, which require notice to the authority before removing a countryside hedgerow and allow it to serve a retention notice where the hedgerow is important under the criteria in the Regulations. There are exemptions, including removal where planning permission has been granted for development, so the sequencing matters: removal before permission is a different legal position from removal after it. The criteria and the notice procedure are set out in hedgerow removal notices and the important hedgerow test.

Biodiversity net gain treats hedgerows in a separate module of the statutory metric with its own trading rules, so metres of hedgerow lost to a splay have to be replaced or enhanced in hedgerow terms. A length of new hedge planted behind the splay, outside the visibility envelope, is the standard answer and should be drawn on the landscape plan rather than promised in text.

Trees within the splay may be protected by an Order or sit in a conservation area, and roadside trees are often in the highway authority's ownership. Check both before including removal in the scheme.

Alternatives where the splay cannot be achieved

In rough order of how often they work:

Move the access. A few tens of metres can transform the geometry, particularly away from the inside of a bend or the crest of a hill.

Use an existing access rather than forming a new one, since an established access with a known collision record is a materially different proposition from a new one.

Reduce the intensity of use. A splay requirement scales with the traffic the access will generate as well as the speed, so a scheme generating a handful of movements a day is judged differently from one generating fifty.

Set the access back behind a widened and lowered verge, where that land is available and the authority will accept the maintenance.

Provide a passing bay and a one-way arrangement, which helps with width rather than with visibility, and is sometimes accepted as part of a package.

Argue a sub-standard splay on the collision record. Request the personal injury collision data for the lane over the preceding five years from the highway authority, and if the record is clean it is a point in your favour. It is a weak point on its own, and authorities are right to say that an absence of recorded collisions on a lightly used lane proves little.

Evidence the highway authority expects

The package that gets a clean consultation response:

• the visibility splay drawing, dimensioned and annotated as described above
• the speed survey data, with the method, dates, location and eighty-fifth percentile results by direction
• a five-year personal injury collision search for the relevant length of lane
• swept path analysis for the largest vehicle that will use the access, which on a farm means an articulated bulk tanker or a combine transporter
• the access construction detail, including gradient over the first few metres and surfacing so that mud and loose material are not carried onto the carriageway
• surface water drainage, showing that runoff does not discharge onto the highway
• land ownership and control over the splay area, with the mechanism securing it
• the hedgerow and tree position, with replacement planting shown

Pull the highway case and the policy case together in a Planning Statement, and where the access serves a diversification proposal rather than a dwelling, align the trip generation with what the business case says, as with farm diversification workshops and offices. An access designed for a house and used by a workshop is the mismatch highway officers notice first.

Enter your postcode on PlanScope to see which documents a new rural access is likely to need.

This is general guidance, not legal advice; check the position with your local planning authority, the local highway authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.