Nottinghamshire visibility splay guidance, June 2026 update.

What the chapter covers

The chapter applies to new development and to changes to existing access arrangements (paragraph 3.1.1). It is to be applied proportionately, having regard to speed, alignment, vehicle mix and usage, and an alternative approach may be accepted where robust evidence shows an equivalent or higher level of safety (paragraph 3.1.2). It covers stopping sight distance, splays at junctions and accesses, forward visibility, agricultural accesses, pedestrian visibility and speed surveys.

Stopping sight distance and design speed

Stopping sight distance is calculated from the 85th percentile wet weather speed, with a reaction time of 1.5 seconds at speeds up to 60 kph (37 mph) and 2.0 seconds above, and deceleration rates that depend on the share of HGVs and on speed (paragraph 3.2.1). Gradient is included in the calculation. Speed and gradient are the normal variables; reaction time and deceleration should not be varied without credible, site-specific evidence (paragraph 3.2.2).

Where speeds were measured in dry conditions, 4 kph (2.48 mph) is deducted to give the wet weather design speed, and the converted speed is the one used in the calculation (paragraphs 3.5.22 to 3.5.25). Figures 3.2.1 and 3.2.2 tabulate the resulting distances by speed, with an allowance for the length of the vehicle bonnet.

Measuring the splay

• X-distance: 2.4 metres in most built-up situations, 4.5 metres for other priority junctions, and no more than 9.0 metres (paragraph 3.3.2).
• Y-distance: equal to the stopping sight distance and measured to the nearside channel of the priority road in each direction (paragraph 3.3.3). It may be measured to the centreline where a refuge or central reservation prevents vehicles crossing it (paragraph 3.3.4).
• Wheel track: Y may be plotted along the inside wheel track, but its position must not be overestimated (paragraph 3.3.12).
• Bends: junctions on the inside of bends should be avoided, and additional splay areas may be needed on the outside of a bend (paragraphs 3.3.6 and 3.3.7).
• Heights: a driver's eye height of 1.05 to 2.0 metres, with the view kept clear down to 0.6 metres, or 0.26 metres above 60 kph (paragraph 3.3.8).
• Land: splays are to lie within the public highway or land the developer controls, with hedges kept at least 1.0 metre back where growth could encroach (notes to section 3.3).

Forward, agricultural and pedestrian visibility

Forward visibility should equal at least the stopping sight distance, measured along the inner lane on curves, and the chapter sets out a step-by-step method for plotting it around a bend (paragraphs 3.3.9 and 3.3.10). On bus routes and classified roads, stopping sight distance is to be provided on the approaches to a new junction over 1.5 times the stopping sight distance. Where vertical visibility is in doubt, a topographical survey and long sections may be needed (paragraph 3.3.11).

For new or intensified agricultural accesses, visibility is assessed from a tractor driver's eye height of 2.0 to 2.2 metres and an x-distance of 4.5 metres measured from the front of the tractor and any equipment. The higher eye position does not remove the need for the full stopping sight distance (paragraphs 3.4.1 to 3.4.4).

Pedestrian visibility splays are usually needed at private accesses with moderate to high pedestrian activity, kept clear above 0.6 metres (paragraph 3.3.13). The chapter recognises that their absence may lead drivers to emerge more cautiously, and the need is to be decided proportionately, having regard to vehicle frequency, pedestrian activity and footway width (paragraph 3.3.14).

Speed surveys

Section 3.5 sets out the highway authority's expectations of speed data in detail. Surveys should record free-flowing traffic on normal weekdays, avoiding congestion, roadworks and events (paragraphs 3.5.6 to 3.5.8). The main requirements are:

• Periods: normally at least two representative periods of about two hours, on different days and at different times, with weekday off-peak periods such as 10:00 to 12:00 and 14:00 to 16:00 likely to be suitable (paragraphs 3.5.12 to 3.5.16).
• Sample: normally at least 200 observations per direction in each period, with the period extended or added to if that is not reached (paragraphs 3.5.17 and 3.5.18).
• Calculation: the 85th percentile is calculated for each period and direction from individual observations; averaged or pre-aggregated values are unlikely to be accepted, and the highest relevant 85th percentile is used (paragraphs 3.5.19, 3.5.20 and 3.5.26).
• Continuous counts: automatic traffic count data should not be treated as one undifferentiated dataset, and any excluded periods should be identified and justified (paragraphs 3.5.10 and 3.5.11).
• Reporting: location, dates, times, equipment, filtering, sample sizes, conditions and the adopted design speed in mph and kph, with individual data available for verification (paragraphs 3.5.27 to 3.5.32).

The highway authority will take a precautionary approach. Where data is not robust, it may request further surveys, reject the data or assume higher speeds (paragraphs 3.5.34 and 3.5.35).

Practical points

• Plan the survey around section 3.5. The expectation is two discrete periods, 200 observations per direction in each, and results reported by period and direction. A single figure from a week-long count may need to be reprocessed.
• Record the weather and show the wet weather conversion where speeds were measured in dry conditions.
• Show the workings from design speed to stopping sight distance and splay, as paragraph 3.5.30 asks.
• Check land control for the full splay, including any additional area needed on the outside of a bend.
• Consider forward visibility on bends and classified roads, as well as the splay at the access itself.