splay
A widening of a minor road where it forms a junction with a major road to ensure that the view of traffic on the major road by drivers on the minor road is not obstructed.
splay: a junction widening that clears the view
A splay is a triangular widened section of pavement where a minor road meets a major road, angled to remove obstructions from the sightline of drivers turning onto the major carriageway. The splay extends the road surface outward from the corner, creating an unobstructed cone of vision so that a driver leaving the minor road can see approaching traffic before committing to the junction.
The typical splay is cut at 45 degrees to the minor road centreline, though angles vary between 30 and 60 degrees depending on local road design standards and the speed environment of the major road. A minimum splay depth (measured perpendicular from the minor road edge) of 2.4 to 3 metres is common in UK guidance, though higher-speed roads require longer splays to give drivers adequate reaction time. The splay widens the junction footprint, consuming verge or property land at the corner.
Splays are created by removing or setback kerbing, cutting back hedgerows, moving fence lines, or demolishing small structures. The cost of land acquisition or legal agreements to create a splay can be substantial on congested routes where buildings or utilities sit close to the junction. On rural roads, splays may require tree felling or drainage redesign.
Sight distance and traffic control
The effectiveness of a splay depends on actual sight distance, which can be defeated by parked vehicles, overgrown vegetation, or architectural features on the opposite side of the major road. Traffic authorities measure the required splay geometry using sight distance calculations based on approach speed and stopping distance. A splay that appears adequate at design time may become insufficient if traffic speed on the major road increases or if vegetation encroaches.
Splays are distinct from other junction treatments: they differ from traffic islands, which control flow through roundabout geometry, and from slip roads, which are full parallel lanes. A splay is passive and costs-effective compared to signalisation or physical traffic calming, making it standard practice in rural and suburban road hierarchies where major roads intersect minor access roads.