Visibility splays – what every property developer should know

Visibility splays play an important role in the design of an access or junction. According to Motion’s Phil Bell, “they are undoubtedly the most important safety component of any priority junction”.

Visibility splays enable drivers on a side road to see vehicles approaching on the major road. They also allow drivers on the major road to see vehicles emerging from the side road. The Highway Authority generally seeks to ensure that visibility splays at junctions are maintained in perpetuity. Often the splays are secured by the Highway Authority through adoption of the land as public highway. They may also be secured by planning condition, although this is less common.

Property developers should consider the following points in relation to their scheme:

1. Visibility splays can unlock a site for development by influencing access location

2. Several factors affect the design of visibility splays, including vehicle speed, reaction time, deceleration rate and gradient

3. Visibility splays, and particularly the deceleration rate, should assume a wet road surface

4. Design criteria may differ for junctions adjoining residential streets, compared to trunk roads

5. Two measurements are taken when designing a visibility splay: the X and Y distances

6. The X distance is the distance from the nearside edge of the carriageway to the driver’s eye-line. In most built-up areas an X distance of 2.4 metres is sufficient

7. The Y distance is the distance over which clear visibility is needed to enable the emerging driver to see approaching main road traffic, and for drivers of those vehicles to see the emerging vehicle

8. Land within visibility splays should generally be kept clear of obstructions above a certain height. Street furniture and some clear stemmed trees are likely to be acceptable, depending on where they are positioned within the splay

9. The guidance on visibility splays can be subjective and recommendations can vary by Highway Authority

10. Visibility splays cannot easily be ‘retro-fitted’ – early consultation with a transport planning consultant is critical to achieving the optimum outcome

If you would value a preliminary discussion about the transport, traffic or infrastructure issues associated with a potential development project, why not give us a call on 01483 531300?


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