Farm access onto a rural road: visibility evidence

A new or improved farm access onto a rural road is decided on visibility evidence, and the evidence has to be measured rather than estimated. The highway authority wants to know how fast traffic actually travels past the site, what a driver emerging can see at that speed, and whether the land needed to keep that view clear is under the applicant's control. Get those three right and most rural access applications are straightforward.

The common failure is assuming the speed limit. A 60 mph limit on a lane where traffic averages 38 mph produces one answer, and an assumption of 60 mph produces a splay nobody can deliver.

What the highway authority is assessing

The local highway authority is consulted on the application and will look at whether an access can be formed and used safely at that point on the network. For an agricultural access that means the geometry of the junction, the sight lines in both directions, the surface and drainage of the first few metres, the swept path of the largest vehicle using it, and whether vehicles wait on the carriageway while gates are opened.

Where the road is a trunk road or motorway slip, National Highways is the relevant body instead and its standards are stricter. On an ordinary county road, the local authority's own design guide applies, and those guides differ enough that the first call should be to the highway officer rather than to a drawing.

Measuring approach speeds rather than assuming the limit

Design standards derive the visibility requirement from the speed traffic actually travels, usually expressed as the 85th percentile wet weather speed. That figure comes from a speed survey: automatic traffic counters or radar equipment recording free flowing traffic over a period of days in each direction, at a position representative of the approach to the access.

Do the survey before the design. It costs less than redrawing the scheme, and a survey that shows lower speeds than the limit can reduce the visibility requirement substantially. Surveys taken during harvest, in school holidays or over a bank holiday will be challenged, so agree the dates with the highway officer if you can.

Where a survey is impractical, some authorities accept the speed limit as a conservative assumption. That is a choice to make knowingly, because it usually means a longer splay and more hedge to remove.

Visibility splay geometry and where it is measured from

A splay is described by two dimensions. The X dimension is the set back from the edge of the carriageway to the point where the driver's eye is assumed to be, commonly 2.4 metres for an ordinary access and sometimes reduced for a lightly used field gate. The Y dimension is the distance visible along the carriageway in each direction, taken from the stopping sight distance appropriate to the measured speed, using Manual for Streets on lower speed roads and the Design Manual for Roads and Bridges on higher speed ones.

Both dimensions are measured to a defined eye height and object height, and the splay is a triangle that must be kept clear of anything above about one metre. Show it on a scaled plan with the dimensions written on, the eye position marked, and a note of the speed the Y distance derives from. Officers reject drawings where the splay is drawn but the assumptions are not stated.

Levels matter on sloping ground. A splay that works in plan can be blocked by a bank or a rising verge, so a section through the critical direction is worth drawing.

Land control within the splay

The splay has to be deliverable, which means the land within it is either in the applicant's control, within the highway boundary, or covered by an agreement with the owner. Verges usually belong to the highway authority, which helps, but hedges and banks on the field side generally belong to the landowner.

Where the splay crosses land you do not own, serve the correct notice and complete the right ownership certificate with the application. Certificate B applies where another owner is involved, and getting this wrong can invalidate a permission. Our note on ownership certificates and agricultural notices sets out who has to be notified, including tenants.

Expect a condition requiring the splays to be provided before the access is used and kept clear of obstruction above a stated height in perpetuity. That condition binds the land, so it affects future hedge management.

Hedgerows, banks and maintenance obligations

Removing hedgerow to form a splay is rarely a free action. Countryside hedgerows may be protected under the Hedgerows Regulations 1997, which require notice to the local planning authority before removing a stretch of qualifying hedgerow, and a hedge can qualify on historical, wildlife or landscape criteria. Removal without notice is an offence.

Timing is the other constraint. Hedgerow cutting and removal during the bird nesting season, broadly March to August, risks breaching the Wildlife and Countryside Act 1981, so programme the work outside it or have an ecologist supervise.

Where hedge loss is substantial, replacement planting set back behind the splay is the usual answer, and on a prominent site a landscape and visual impact assessment may be proportionate. Set back planting also solves the maintenance problem, because a hedge planted on the splay line will obstruct it again within a few seasons.

Agricultural vehicle tracking and gate setbacks

Farm accesses fail on turning as often as on visibility. Track the largest vehicle that will use the access, which on most holdings is a tractor and trailer or an articulated feed lorry rather than a pickup, and show the swept path entering and leaving in both directions.

Set the gate back far enough that the longest vehicle can stand wholly clear of the carriageway while the gate is opened and closed. Many authorities specify a minimum set back for this, and where they do not, the tracking drawing is the justification. Gates should open inwards, never over the highway.

Bell mouth radii, the width of the access throat and the first stretch of surfacing all follow from the same tracking exercise. A radius that suits a car forces a trailer to swing across the opposing lane.

Surfacing and drainage at the entrance

Two conditions appear on almost every rural access permission: a bound surface for the first several metres to stop loose material being carried onto the carriageway, and drainage arranged so that surface water does not discharge onto the highway. Both cost little at design stage and a lot to retrofit.

Forming or altering a vehicle crossing over a verge or footway is separate from planning permission and needs the highway authority's consent under the Highways Act 1980, with the works carried out to its specification. Larger schemes may need an agreement under section 278 for works in the highway. Budget for the authority's fees and inspection charges.

Evidence to submit

The pack that gets a clean consultee response contains a location plan, a scaled access drawing with splays dimensioned and assumptions stated, the speed survey results, a swept path drawing for the design vehicle, a section where levels are relevant, details of surfacing and drainage, and a short note on hedgerow removal and replacement with the nesting season addressed.

Add the planning statement explaining why the access is needed, since agricultural justification carries weight in the countryside. Where the access serves a diversification use rather than farming, say so plainly, because the trip pattern and therefore the highway assessment are different.

PlanScope drafts the narrative documents and flags where site measurements are missing. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. Speed surveys, tracking drawings and splay design should come from a suitably qualified highway or transport consultant.

This is general guidance, not legal advice, and highway standards vary between authorities. Check the position with your local planning authority and highway authority before relying on it. Enter your postcode on PlanScope to see which supporting documents your access application is likely to need.