The 3-Second Rule & Safe Following Distance
The car in front brakes without warning on a busy expressway. You're doing 100 km/h, following close. You react, you brake — but it's not enough. Rear-end collisions are almost entirely caused by following too closely, and almost entirely preventable. The 3-second rule is your first line of defence.
How to Measure the 3-Second Gap
Choose a fixed point ahead — a bridge pillar, an overhead sign, a tree at the roadside. The moment the vehicle in front passes that point, begin counting: 'one-thousand-one, one-thousand-two, one-thousand-three.' If your vehicle reaches that point before you finish counting, you are too close. Increase your speed gap slightly or ease off until you can comfortably complete the count. The gap you open corresponds roughly to your vehicle's stopping distance in normal conditions.
The 3-second rule applies on dry roads with good visibility. Double it to 6 seconds in rain, fog, or at night — conditions that both reduce your visibility and increase stopping distance. On a highway at 100 km/h, 6 seconds corresponds to approximately 167 metres — about 16 car lengths. This sounds like a lot, but it is the scientifically minimum safe gap in those conditions.
Why Trucks Need Extra Gap
A fully loaded truck weighing 40 tonnes requires significantly more distance to stop than a 1.5-tonne car. Trucks also have air brake systems with a measurable delay from pedal press to brake application. At highway speeds, a truck may need up to 150 metres to stop. Following a truck at only 20 metres is catastrophic — when it brakes hard, your car will go underneath it. Give trucks at least 4–5 seconds of following distance.
Motorcycles — Less Mass Means More Braking Uncertainty
Two-wheelers have less mass but also less braking friction than four-wheelers. More critically, a motorcyclist may swerve or emergency-brake to avoid a pothole or debris that your car would simply roll over. This means motorcycles can stop or change direction more abruptly and unexpectedly. Maintain at least a 3-second gap behind motorcycles, more in wet conditions where their stability is reduced.
If a driver is following you too closely, do not brake-check them — this is aggressive, dangerous, and legally puts you at fault. Instead: signal and gradually move left if another lane is available. If not, gently reduce your speed to increase the gap in front of you, giving yourself more stopping room. This way, if the tailgater hits you, you have maximised the chance that you won't hit the car ahead. Never engage or make eye contact with an aggressive tailgater.
recommended minimum following gap at 100 km/h in good conditions
Equivalent to approximately 6 car lengths on an expressway
Source: Based on 2-second rule at 100 km/h (27.8 m/s × 2 = 55.6 m)
You are driving behind a truck on a national highway at 80 km/h in light rain. What is the appropriate following distance?
Tap an option to reveal the answer
- ✓Use the 3-second rule: count from when the car ahead passes a fixed point to when you reach it.
- ✓Double to 6 seconds in rain, fog, or night driving.
- ✓Trucks need 4–5 seconds minimum — they weigh up to 40 tonnes and have air brake delay.
- ✓If tailgated, don't brake-check. Move left gradually and slow to create space ahead.
- ✓At 100 km/h the minimum safe following gap is approximately 60 metres — about 6 car lengths.
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