Safety Margins

Safety margin is defined as the space that needs to be left between your vehicle and the one in front so that an accident will not be caused if it slows down or stops suddenly. Safety margins are also referred to as ‘separation distances’.The safety margins dealt with in this section are primarily refer to following distances and stopping distances of vehicles. A following distance is the space left between your car and the vehicle ahead. Stopping distances include the combined reaction time and braking distance, once you realise you have to stop.

Weather and General Issues

Hot Weather, Fog and Wind

• Hot weather can cause the road surface to soften, affecting tyre grip and braking
• In foggy conditions always use dipped headlights, slow down, allow more time for your journey and increase the gap to the vehicle in front of you
• Side winds are most likely to occur on an open road and you should take care when passing cyclists and motorbikes, giving them extra room.

Wet Weather

• The braking distance is at least twice as normal in wet weather, and the four second rule should be adhered to
• Heavy rain can make the steering feel lighter, and you should ease off the accelerator to avoid the risk of aquaplaning
• Driving through deep water may affect your brakes, and you should dry them off by going slowly and applying them gently
• Dipped headlights should be used in the case of motorway spray during heavy rain

Icy Weather

• Before starting a journey, you must clear any ice or snow from windows, mirrors, lights and number plates
• When driving off in snow, you should use the highest gear you can to prevent the wheels from spinning
• The braking distance on ice is at least ten times longer than normal, and you should brake gently and in plenty of time
• If approaching a sharp bend in snowy conditions, you should slow down and avoid sudden steering movements
• If the steering suddenly feels light, this could be an indication of black ice on the road, and you should ease off the accelerator

General Safety Issues

• When approaching a right hand bend, you should keep well to the left to improve your view of the road ahead
• Be aware that coasting i.e. travelling long distances in neutral, reduces driver control
• When driving down a steep hill, select a lower gear and use your brakes carefully to control your speed
• When parking facing downhill, you should turn the wheels towards the kerb and apply the handbrake
• The most common cause of skidding is known to be driver error

Stopping Distances and Brakes

The definition of the overall stopping distance is the combination of thinking and braking.

• 20 mph – Thinking 6m + Braking 6m = 12m
• 30 mph – Thinking 9m + Braking 14m = 23m
• 40 mph – Thinking 12m + Braking 24m = 36m
• 50 mph – Thinking 15m + Braking 38m = 53m
• 60 mph – Thinking 18m + Braking 55m = 73m
• 70 mph – Thinking 21m + Braking 75m = 96m

Contraflow Systems

• Reduce speed
• Select the appropriate lane in plenty of time
• Keep the correct separation distance

Anti-Lock Brakes

• They are of most use when stopping quickly in an emergency
• They permit the vehicle to be steered when braking hard
• The anti-lock system begins to work after you have applied maximum brake pressure, just before the wheels lock
• As they prevent the wheels from locking, you are less likely to skid when emergency braking
• Proper use requires you to brake rapidly and firmly until you have stopped or slowed down

Safety Margins Theory Test Tips

There is no option other than to learn the stopping distances off by heart, using the principle that the faster you are travelling, the further it takes you to stop. There may be questions about anti-lock braking systems, and you should have some knowledge as to how they work.