Visibility and Road Hazards - DGT theory chapter with practice test

Driving Manual · Theory

Chapter 12 - Visibility and Road Hazards

Visibility is one of the most critical factors in road safety. If a driver cannot see clearly, or cannot be seen by others, the risk of an accident rises sharply. This chapter covers the causes of reduced visibility, how to handle each condition, and the road hazards every driver must recognise.

Split-scene illustration: left half shows a clear road in bright daylight with full visibility; right half shows the same road in dense fog with no visible lane markings or horizon — Good visibility versus poor visibility - the difference can be life or death.

12.1 Importance of Visibility

Visibility is one of the most critical factors in road safety. If a driver cannot see clearly, or cannot be seen by others, the risk of a traffic accident increases significantly. Visibility conditions determine how quickly a driver can detect obstacles, assess situations, and respond appropriately.

Two side-by-side top-down diagrams of a driver at the wheel: left shows a wide, clear cone of vision on a bright road; right shows a severely narrowed cone in fog or at night — Good visibility gives a wide cone of perception - fog or darkness cuts it dramatically.

12.2 Main Causes of Reduced Visibility

Reduced visibility may occur due to several factors:

Weather conditions: fog, heavy rain, snow, smoke, or dust clouds.
Light conditions: twilight, night-time, glare from sun or headlights.
Road design: tight curves, crests (summits), tunnels, or poorly lit areas.
Vehicle issues: fogged or dirty windshields, non-functional lights, or poor ventilation.

A fog and heavy rain cloud icon representing weather-related visibility reduction — Weather

A sun glare icon with radiating beams representing glare and low-light visibility issues — Light conditions

A winding road with a hill crest icon representing curves and crests that block the driver's view — Road design

A dirty or fogged windshield icon representing vehicle-related visibility issues — Vehicle issues

12.2.1 Poorly Lit Roads

A road is considered poorly lit when a driver cannot read a licence plate from 10 metres or distinguish a dark-coloured vehicle from 50 metres away.

Diagram of a dark road showing a car with two distance markers: a 10 m arrow pointing to a licence plate, and a 50 m arrow pointing to a dark vehicle silhouette in the distance — A road is poorly lit if you cannot read a plate at 10 m or see a dark vehicle at 50 m.

12.3 Types of Visibility Impairment

12.3.1 Fog

Reduces visibility drastically and suddenly. Use dipped headlights and front/rear fog lights if necessary. Avoid high beams - they reflect off fog particles and worsen visibility.

First-person driver's view through a windshield into thick fog: only a few metres of road visible, dipped headlight beams reflected back by the fog, illustrating why high beams are counterproductive — In fog, high beams reflect back and reduce visibility further - always use dipped headlights.

12.3.2 Rain and Snow

Wipers and defoggers must work properly. Reduce speed and increase braking distance. Use dipped headlights during the day for better visibility.

Driver's view through a rain-covered windshield with wipers active, or a snowy road scene ahead with reduced visibility and a longer braking-distance arrow overlay — Rain and snow demand working wipers, reduced speed, and increased following distance.

12.3.3 Night Driving

Use dipped beams in urban areas; use high beams on poorly lit rural roads without dazzling others. Switch to dipped beams when another vehicle approaches or is ahead of you.

Side diagram or top-down view showing two scenarios: a car using high beams on an empty dark road, then switching to dipped beams as an oncoming car appears. Beam reach arrows labelled for each scenario. — High beams on empty roads - switch to dipped beams when another vehicle appears.

12.3.4 Sun Glare

Use sun visors and polarised sunglasses. Keep the windshield clean inside and out to avoid light scattering.

Split image: left shows a driver with a sun visor pulled down facing a low sun; right shows a dirty windshield scattering sunlight versus a clean windshield with clear visibility — Sun visor, sunglasses, and a clean windshield are essential defences against sun glare.

12.4 Use of Vehicle Lights in Low Visibility

Lights should be used to see and be seen.
Dipped headlights are mandatory in poor visibility and in tunnels.
Front fog lights are optional and may be used when visibility is reduced by weather or on narrow, winding roads.
The rear fog light is mandatory in cases of very dense fog, heavy snow, or rain.

Annotated diagram of a car (front and rear view) with labelled arrows pointing to each light type: position lights, dipped headlights, front fog lights, and rear fog light — Know your lights: each serves a specific purpose in low-visibility conditions.

12.4.1 Permitted Combinations

Combination	When to use
Position + dipped beam	Most common in low visibility.
Position + front fog light	Daytime use.
Position + dipped beam + front fog light	Night or poor visibility.
Position + high beam	Only in open areas and at night.

Four car silhouettes in a row, each showing a different active light combination with the lit lights highlighted: (1) position + dipped beam, (2) position + front fog, (3) position + dipped + front fog, (4) position + high beam — Four permitted light combinations - each suited to a different visibility scenario.

12.5 Driving Behaviour in Poor Visibility

Adapt speed to ensure full control of the vehicle.
Keep a longer safety distance from the vehicle ahead.
Use the right lane when visibility is limited.
Avoid sudden braking or steering.
If you must stop, pull off the road and turn on hazard lights.

A foggy road scene with a car in the right lane maintaining a long, clearly visible gap from the car ahead. A second car is shown pulled off the road on the shoulder with hazard lights flashing. — In poor visibility: right lane, long gap, gentle inputs - and pull well off if you must stop.

12.6 Road Hazards

Road hazards are conditions or features that increase the risk of an accident. These are typically signalled with triangular warning signs with red borders.

A red-bordered triangular warning sign planted at the roadside in realistic context, with a road stretching ahead - establishing the visual language of hazard warning signs — Triangular red-border signs warn of hazards ahead - learn to recognise each one.

12.6.1 Common Hazard Types

Sign	Code	Hazard
	P-13a	Dangerous bend to the right.
	P-13b	Dangerous bend to the left.
	P-14a	Series of dangerous bends, first to the right.
	P-14b	Series of dangerous bends, first to the left.
	P-15a	Hump in the road.
	P-15b	Dip in the road.
	P-16a	Steep descent.
	P-16b	Steep ascent.
	P-19	Slippery road surface.
	P-23	Domestic animals crossing.
	P-24	Wild animals crossing.
	P-21a	Children - school or play area nearby.
	P-20a	Pedestrian crossing.
	P-25	Two-way traffic.
	P-26	Falling rocks or landslide area.
	P-29	Crosswind - dangerous for high-sided vehicles.
	P-30	Uneven or soft shoulder - lateral drop-off.
	P-33	Reduced visibility due to environmental conditions.

12.6.2 Additional Hazards

Aquaplaning

A water layer reduces tyre grip and steering control. The tyre loses contact with the road surface, making braking and steering ineffective.

Cross-section diagram of a tyre on a wet road: a wedge of water is shown lifting the tyre away from the road surface, with an arrow indicating loss of contact and steering control — Aquaplaning: water lifts the tyre off the road - you lose braking and steering instantly.

Icy Roads

Ice may be invisible ("black ice") and extremely dangerous. The road surface looks normal but is glazed with a thin transparent ice layer.

A road surface that appears completely normal but has a subtle glassy sheen indicating black ice, with a warning overlay or exclamation marker to highlight the hidden danger — Black ice looks like a wet road - but grip is almost zero. Reduce speed and avoid sudden inputs.

Potholes or Gravel

May cause loss of control or damage to tyres. Loose gravel or unexpected potholes can destabilise the vehicle suddenly.

A tyre encountering a pothole or loose gravel on a road surface, with a destabilisation arrow showing the sudden sideways force on the vehicle — Potholes and gravel cause sudden loss of control - reduce speed and grip the wheel firmly.

12.7 Adapting Speed in Hazardous Zones

Always drive at a speed that allows you to stop within your visible distance.
Respect warning and speed-limit signs - they are placed based on accident statistics and road studies.
On downhill slopes, reduce speed and use lower gears to avoid brake overheating.

A side-view diagram of a car descending a steep slope in a lower gear, with a stopping-distance arc overlaid that exactly matches the visible road distance ahead. Labels: "visible distance" and "stopping distance". — On downhill slopes, use a lower gear and never outrun your visible stopping distance.

12.8 Emergency Situations

If visibility becomes dangerously low:

Pull over to a safe spot as far off the road as possible.
Turn on hazard lights and fog lights.
Use reflective vests if leaving the vehicle.
Never stop in the middle of a lane or without lighting.

A car pulled fully off the road onto the shoulder in dense fog, hazard lights flashing. A driver stands at a safe distance wearing a reflective vest, away from the carriageway. — In an emergency: get completely off the road, hazard lights on, and wear your reflective vest.

12.9 Summary

Visibility determines your ability to react safely - reduce speed when in doubt.
Use proper lighting combinations at all times.
Recognise warning signs for curves, slopes, animals, or adverse conditions.
Be especially cautious in fog, snow, rain, or low-light environments.

A compact 5-icon recap infographic in a row: (1) visibility cone, (2) car with active lights, (3) triangular warning sign, (4) weather icons (fog/rain/snow), (5) stopping distance arrow. Each icon has a short label beneath. — Chapter 12 at a glance: visibility, lights, signs, weather, and stopping distance.

Drive at a speed that lets you stop within the distance you can see.

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Last updated: 2026-06-27

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