Splays - visibility at junctionsSplays – visibility at junctions


The visibility splay is the ability to clearly see traffic approaching from both directions at a junction. 

Visibility splays at any entrance or junction are measured along the edge of the main road (the “Y” distance) from a point a set distance back from the edge of the main road (the “X” distance).

Visibility Splays

Generally the X distance is 2.4m for residential streets and 4.5m for major junctions, busy access roads or where the side road has a speed greater than 40mph etc. The greater distance of the splay might also apply for industrial roads. These distances might vary from highways authority to highways authority. Note that the Local Planning Authority (LPA) might not be the body that sets these.

The Y distance of the splay will vary depending upon the speed of the vehicles and not how busy the road might be. The speed is a measured 85th percentile vehicle speed (mph) and not the speed limit. The 85th percentile speed is defined as, “the speed at or below which 85 percent of all vehicles are observed to travel under free-flowing conditions past a monitored point.” 

Any space within the resulting two triangle areas must remain free of any obstruction above 1 metre. The road curvature may require that the lines in each direction are of different lengths.

Speed Y distance in Metres
Light Vehicles
11 to 15 17
16 to 20 25
21 to 25 33
26 to 30 43
31 to 35 54
36 to 40 65
41 to 44 120
45 to 53 160
54 to 62 215
63 to 75 295

These distances might vary depending upon your local highway department. Check locally for variations for splays in these figures.