Safety margins are the space and time you leave yourself to react: the gap to the vehicle in front, the room you give other road users, and how you adjust both when the weather turns. The theory test asks about stopping distances, the two-second rule, and driving in rain, ice, snow, fog, wind and heat. These are some of the most number-heavy questions in the test, so they’re easy marks once learned.
Last reviewed: September 2026. Checked against the Highway Code and GOV.UK.
What this topic covers in the theory test
Expect questions on:
- typical stopping distances at different speeds, split into thinking and braking distance
- the two-second rule, and how much to increase it in wet and icy conditions
- the four-second gap in tunnels
- skidding, aquaplaning and ABS
- driving in ice and snow, fog, strong winds and hot weather
- safe passing distances for cyclists, horse riders and large vehicles
- keeping control on long downhill slopes
Typical stopping distances
Your overall stopping distance is made up of two parts:
- Thinking distance: how far you travel between seeing a hazard and starting to brake.
- Braking distance: how far you travel from the moment you start braking until you stop.
The Highway Code publishes typical figures for a car in good conditions. These come from the official typical stopping distances chart linked from rule 126, which uses an average car length of 4 metres.
| Speed | Thinking distance | Braking distance | Overall stopping distance |
|---|---|---|---|
| 20 mph (32 km/h) | 6 m | 6 m | 12 m (40 feet), about 3 car lengths |
| 30 mph (48 km/h) | 9 m | 14 m | 23 m (75 feet), about 6 car lengths |
| 40 mph (64 km/h) | 12 m | 24 m | 36 m (118 feet), about 9 car lengths |
| 50 mph (80 km/h) | 15 m | 38 m | 53 m (175 feet), about 13 car lengths |
| 60 mph (96 km/h) | 18 m | 55 m | 73 m (240 feet), about 18 car lengths |
| 70 mph (112 km/h) | 21 m | 75 m | 96 m (315 feet), about 24 car lengths |
Two patterns make these easier to remember. Thinking distance goes up by 3 metres for every 10 mph. Braking distance grows much faster: doubling your speed from 30 to 60 mph roughly quadruples it, from 14 m to 55 m. That’s why a small increase in speed makes a big difference to whether you can stop in time.
These are only typical figures. The chart itself notes the real distance depends on your attention (which affects thinking distance), the road surface, the weather and the condition of your vehicle. Tiredness, distraction, alcohol or drugs all lengthen your thinking distance.
The two-second rule
Rule 126 says you should drive at a speed that will allow you to stop well within the distance you can see to be clear. Leave enough space between you and the vehicle in front so that you can pull up safely if it suddenly slows down or stops. The safe rule is never to get closer than the overall stopping distance.
Because distances are hard to judge, the Highway Code suggests a time gap instead:
- Leave at least a two-second gap on roads carrying faster-moving traffic.
- That gap should be at least doubled on wet roads.
- It may need to be up to ten times greater on icy roads.
- In tunnels, leave a four-second gap. If you have to stop in a tunnel, leave at least a 5-metre gap to the vehicle in front.
To measure it, pick a fixed point such as a sign or lamp post. When the vehicle ahead passes it, say “Only a fool breaks the two-second rule.” If you reach the point before you finish, you’re too close. Large vehicles and motorcycles need a greater distance to stop, so allow more room behind them too. Tailgating is dangerous and illegal.
Wet weather, aquaplaning and skids
Rule 227 says that in wet weather stopping distances will be at least double those required for stopping on dry roads, because your tyres have less grip. Keep well back from the vehicle in front.
If the steering suddenly feels unresponsive, water is probably preventing the tyres from gripping the road. Ease off the accelerator and slow down gradually. This is often called aquaplaning.
Rule 119 explains that skidding is usually caused by the driver braking, accelerating or steering too harshly, or driving too fast for the conditions. If you skid, remove the cause by releasing the brake pedal fully or easing off the accelerator, and turn the steering wheel in the direction of the skid. For example, if the rear of the car skids to the right, steer immediately to the right to recover.
ABS helps in an emergency stop but isn’t magic. Rule 120 says apply the footbrake firmly and don’t release the pressure; ABS should help you keep steering control, but it does not necessarily reduce your stopping distance.
After driving through deep water, rule 121 says test your brakes at the first safe opportunity by pushing gently on the pedal, then apply light pressure while driving slowly to dry them.
Ice and snow
Rule 228 says don’t drive in these conditions unless your journey is essential. If you must, clear all snow and ice from your windows, lights, number plates and mirrors, and make sure the windows are demisted (rule 229).
When driving on ice or snow:
- drive with care even if the roads have been treated, and keep well back from the road user in front, because stopping distances can be ten times greater than on dry roads (rule 230)
- avoid sudden actions, as these could cause loss of control (rule 231)
- drive at a slow speed in as high a gear as possible; accelerate and brake very gently (rule 231)
- drive particularly slowly on bends, where loss of control is more likely, and brake progressively on the straight before you reach the bend (rule 231)
- steer smoothly and gently round corners
- check your grip on the road surface when there is snow or ice by choosing a safe place to brake gently (rule 231)
Fog, wind and hot weather
Fog: rule 226 says you must use headlights when visibility is seriously reduced, generally when you can’t see for more than 100 metres. You may also use front or rear fog lights, but you must switch them off when visibility improves. Before entering fog, check your mirrors and slow down, and make sure you can pull up well within the distance you can see (rule 234 to rule 236). Keep a safe distance behind the vehicle in front.
Wind: high-sided vehicles are most affected by windy weather, but strong gusts can also blow a car, cyclist, motorcyclist or horse rider off course (rule 232). Take extra care when passing them. Motorcyclists are particularly affected by turbulence from large vehicles (rule 233).
Hot weather: rule 237 says keep your vehicle well ventilated to avoid drowsiness. Be aware that the road surface may become soft, and that if it rains after a dry spell the road may become slippery, affecting your braking and steering.
Space for other road users and hills
Safety margins aren’t only about the vehicle ahead. Rule 163 says:
- leave at least 1.5 metres when overtaking cyclists at speeds of up to 30 mph, and give them more space at higher speeds
- pass horse riders and horse-drawn vehicles at speeds under 10 mph and allow at least 2 metres of space
- give motorcyclists, cyclists and horse riders at least as much room as you would when overtaking a car
Behind large vehicles, rule 164 says drop back. This increases your ability to see ahead and lets the driver see you in their mirrors. Rule 222 gives similar advice: pull back to increase your separation distance.
On long downhill slopes, rule 160 says select a lower gear to help control your speed. That uses engine braking instead of relying on the footbrake alone, and rule 122 explains why coasting in neutral reduces your control.
Common mistakes learners make
- Mixing up thinking and braking distance. Thinking distance comes first and grows slowly; braking distance grows fast.
- Remembering the dry-road figures but forgetting to double the gap in the wet.
- Assuming ABS always shortens stopping distance.
- Braking on a bend in icy weather instead of slowing down on the straight beforehand.
- Using fog lights in light drizzle and leaving them on after the fog clears.
- Passing a cyclist too closely because there’s an oncoming car.
- Following close behind a lorry, where you can’t see what’s ahead.
Quick-reference table
| Condition | Minimum gap / rule | Highway Code |
|---|---|---|
| Dry, faster roads | At least 2 seconds | rule 126 |
| Wet roads | At least double (4 seconds or more) | rule 126, rule 227 |
| Icy roads | Up to 10 times greater | rule 126, rule 230 |
| Tunnels | 4 seconds; at least 5 metres if stopped | rule 126 |
| Fog | Headlights when visibility under 100 m | rule 226 |
| Overtaking a cyclist, up to 30 mph | At least 1.5 metres | rule 163 |
| Passing a horse rider | Under 10 mph, at least 2 metres | rule 163 |
Practice questions
These practice questions are written by Get Driving Test Ready to help you revise. They are not official DVSA questions.
Q1. What is the typical overall stopping distance for a car at 30 mph in good conditions?
A) 53 metres
B) 23 metres
C) 36 metres
D) 12 metres
Answer: B. At 30 mph the typical overall stopping distance is 23 metres (75 feet): 9 m thinking distance plus 14 m braking distance. (Highway Code rule 126)
Practise this on the road: In a quiet 30 mph street, pick a fixed point and discuss with your instructor whether you could stop within 23 metres.
Q2. What is the typical overall stopping distance at 70 mph on a dry road?
A) 73 metres
B) 53 metres
C) 96 metres
D) 120 metres
Answer: C. At 70 mph the typical overall stopping distance is 96 metres (315 feet), about 24 car lengths. (Highway Code rule 126)
Practise this on the road: On a faster road, discuss with your instructor how far ahead you need to look to stop safely at higher speeds.
Q3. At 50 mph, what is the typical thinking distance?
A) 38 metres
B) 15 metres
C) 21 metres
D) 9 metres
Answer: B. At 50 mph the typical thinking distance is 15 metres. The braking distance is 38 metres, giving 53 metres overall. (Highway Code rule 126)
Practise this on the road: Practise commentary driving on a 50 mph road, saying hazards aloud early to cut your thinking time.
Q4. It's raining heavily. How should you change the gap to the vehicle in front?
A) Increase it to ten times the normal gap
B) Halve it, so you can see past the vehicle
C) Keep the normal two-second gap
D) At least double it
Answer: D. The two-second gap should be at least doubled on wet roads, because stopping distances are at least double those on dry roads. (Highway Code rule 126)
Practise this on the road: On a wet day, practise leaving at least a four-second gap by counting past a fixed point.
Q5. How much greater can stopping distances be on icy roads compared with dry roads?
A) Up to ten times
B) Up to twice
C) Exactly the same with ABS
D) Up to three times
Answer: A. On icy roads stopping distances can be ten times greater than on dry roads, so keep well back. (Highway Code rule 230)
Practise this on the road: In icy or frosty weather, talk through with your supervisor how you would increase your gap and drive gently.
Q6. You're driving a car through a tunnel. What is the minimum time gap the Highway Code says you should leave to the vehicle in front?
A) Half a second
B) Two seconds
C) No gap is needed because tunnels have lower speed limits
D) One second
Answer: B. Rule 126 says allow at least a two-second gap on high-speed roads and in tunnels, where visibility is reduced. Drivers of large vehicles should leave four seconds in a tunnel. If you have to stop in a tunnel, leave at least 5 metres to the vehicle in front. (Highway Code rule 126)
Practise this on the road: If you drive through a tunnel, practise keeping at least a two-second gap and following the tunnel's own signs and lights.
Q7. Your steering suddenly feels very light while driving through heavy surface water. What should you do?
A) Brake firmly
B) Change to a lower gear and accelerate
C) Ease off the accelerator and slow down gradually
D) Steer sharply towards the kerb
Answer: C. Unresponsive steering in the wet means water is stopping the tyres gripping the road. Ease off the accelerator and slow down gradually. (Highway Code rule 227)
Practise this on the road: On wet roads, practise easing off the accelerator early before standing water rather than braking in it.
Q8. You're overtaking a cyclist on a 30 mph road. What is the minimum space you should leave?
A) 1.5 metres
B) 3 metres
C) 1 metre
D) 0.5 metres
Answer: A. Leave at least 1.5 metres when overtaking cyclists at speeds of up to 30 mph, and more at higher speeds. (Highway Code rule 163)
Practise this on the road: When passing cyclists in town, practise checking your road position so you leave at least 1.5 metres.
Q9. When should you use headlights because of fog?
A) Only on motorways
B) Only after sunset
C) Whenever there is any mist
D) When visibility is seriously reduced, generally when you can't see for more than 100 metres
Answer: D. You must use headlights when visibility is seriously reduced, generally when you can't see for more than 100 metres. (Highway Code rule 226)
Practise this on the road: Find your headlight and fog light switches, and discuss with your instructor how to judge 100 metres of visibility.
Q10. You're driving on an icy road and approaching a bend. When should you slow down?
A) On the straight, before you reach the bend
B) There's no need to slow down in a high gear
C) As you leave the bend
D) In the middle of the bend
Answer: A. On ice, brake gently and progressively on the straight before you reach a bend, and take the bend particularly slowly. (Highway Code rule 231)
Practise this on the road: On bends, practise doing all your braking on the straight before the bend, then steering smoothly through it.
Next steps
Go back to the theory test hub for all 14 topics. Related topics: vehicle handling, which covers control in different conditions, and motorway rules, where following distances matter most at speed. For the signs that warn of slippery roads, crosswinds and ice, see our warning signs guide.