How to Draw Visibility Splays on Plans – A Guide for Architects and Planners.

Visibility splays are one of those small details that can have a big impact on a planning application. If they are missing, incorrectly drawn, or based on the wrong standard, they can quickly lead to highways comments, revised drawings, delay, or additional consultant input.

For architects, planners and developers, showing visibility splays correctly at an early stage can help demonstrate that a proposed access is safe, deliverable and unlikely to create an unacceptable highway safety issue.

What is a visibility splay?

A visibility splay is the area of land that needs to be kept clear so that a driver emerging from a site access can see approaching traffic, cyclists and pedestrians — and so that other road users can see the vehicle emerging.

On a plan, it is usually shown as a triangular area extending from the proposed access along the highway in both directions. The required dimensions depend on the type of road, traffic speeds, the nature of the access, and the relevant design guidance.

Why visibility splays matter in planning applications

Highway authorities will often check visibility splays when reviewing planning applications for new or altered accesses. This can include residential driveways, commercial accesses, care homes, schools, industrial sites and changes of use.

If the required visibility cannot be achieved, the authority may ask for amendments to the site layout, changes to boundary treatments, relocation of walls, fences or landscaping, or further technical justification.

Getting the splays right at the design stage can help avoid:

• delays during the planning process;
• requests for revised plans;
• late-stage changes to the access arrangement;
• unexpected land ownership issues; and
• highways objections that could have been avoided.

Which guidance applies?

In many local authority situations, visibility splays are considered with reference to Manual for Streets or local highway design guidance. For higher-speed roads, trunk roads or more strategic highway environments, other guidance such as the Design Manual for Roads and Bridges may be relevant.

The correct standard is not always determined by speed limit alone. Highway authorities may also take account of measured traffic speeds, road classification, forward visibility, collision history, pedestrian activity and the character of the street.

For that reason, the example below should be treated as a typical starting point rather than a rule that applies to every site.

How to draw a typical 2.4m x 43m visibility splay for an access onto a 30mph road

For a simple access onto a 30mph local road, a commonly used starting point is a 2.4m x 43m visibility splay. This means:

• the X-distance is 2.4m, measured back from the edge of the carriageway into the site; and
• the Y-distance is 43m, measured along the road in each direction.

To draw this on a plan:

1. Identify the centreline of the proposed access. Where it meets the carriageway is the starting point.
2. Measure 2.4m back from the edge of the carriageway along the centreline of the access. This is the driver’s eye position.
3. From the same starting point, at the edge of the carriageway, draw lines to points 43m along the nearside kerb line in each direction.
4. From the end of those lines, draw new lines to the driver’s eye position.
5. The triangular areas formed by the three lines are the visibility splays.
6. Check whether anything within those splays would obstruct visibility, such as walls, fences, hedges, parked vehicles, signs, street furniture or changes in level.
7. Check whether the land within the splay is either within the applicant’s control or forms part of the adopted highway.

As a general principle, visibility within the splay should be kept clear of obstructions that would materially affect intervisibility between drivers and other road users. Boundary treatments, landscaping and levels should therefore be considered carefully at the earliest stage.

Common mistakes when drawing visibility splays

Some of the most common problems we see include:

• measuring the Y-distance from the wrong point;
• drawing visibility to the centreline of the road rather than along the nearside kerb line;
• using a standard 2.4m x 43m splay where a different distance is required;
• showing splays across third-party land without confirming control;
• forgetting to check boundary walls, fences, hedges and proposed planting;
• using the speed limit rather than measured traffic speeds where speed survey data is needed; and
• showing splays on a plan that is not to scale or not based on an accurate topographical survey.

These issues are often simple to fix early on, but can become much more difficult once the site layout has been developed around an access arrangement that does not work.

When should you get transport planning advice?

For straightforward accesses, architects are more than capable of plotting simple visibility splays themselves. However, professional transport planning input is often worthwhile where:

• the site is on a busy or constrained road;
• visibility is substandard or borderline;
• the access is close to a bend, junction, crossing or bus stop;
• third-party land may be involved;
• there is a steep change in levels;
• the proposal includes commercial, care, school or residential development;
• the highway authority has already raised concerns; or
• speed survey evidence may be required.

At Fastnet Transport Planning, we prepare visibility splay drawings, swept path analysis, access appraisals, and Transport Statements to support planning applications and resolve highways issues before they become planning risks.

Need help with visibility splays?

If you are preparing a planning application and need visibility splays checked, drawn or justified, we can help. We regularly work with architects, planners, developers and landowners to review access arrangements and provide clear, practical highways advice.

Contact Fastnet Transport Planning for early advice before your layout is fixed, or for support responding to highways comments on a live planning application.