Following distance

By the end of this topic you can

• You can measure a two-second gap using a fixed point at the roadside.
• You can double the gap in wet weather and increase it further in ice, snow or fog.
• You can rebuild your gap smoothly when someone pulls into it.
• You can explain why stopping distance grows so quickly with speed.
• You can deal calmly with a driver tailgating you.

What you need to know and understand

• Keep at least a two-second gap in the dry and at least four seconds in the wet.
• In snow, ice or fog you may need a much bigger gap, and a slower speed.
• RSA minimum stopping distance for a car at 50 km/h: about 25 metres dry and 36 metres wet.
• At 100 km/h the RSA minimum is about 70 metres dry and 121 metres wet.
• These figures are minimums. Real stopping distances are often longer.
• In a road tunnel the recommended minimum gap for a car is 50 metres.
• At 120 km/h the RSA minimum stopping distance in the dry is about 102 metres.

How to count two seconds

1. Pick a fixed point ahead, such as a lamp post, sign or bridge.
2. When the back of the vehicle in front passes it, start a two-second phrase. The RSA suggests 'Only a fool breaks the two-second rule'.
3. If you reach the point before you finish the phrase, you are too close. Ease off and count again.
4. In the wet, say the phrase twice to make four seconds.

Why speed changes everything

Stopping distance is your thinking distance plus your braking distance. Thinking distance grows in step with speed, but braking distance grows much faster: in the RSA tables, doubling your speed makes the braking distance about three to four times longer. Using seconds works because the gap in metres grows automatically as you go faster.

On a wet road, braking distances are much longer, which is why the gap should at least double. Rain, worn tyres and a heavy car all add metres. Tiredness, alcohol, drugs and distraction slow your reaction and add metres before you even touch the brake.

Tailgating: giving and getting

• Do not follow closely to pressure a slower driver. It is dangerous and intimidating, and it leaves you no time to stop.
• If someone pulls into your gap, ease off smoothly to rebuild it. Do not brake hard.
• If someone tailgates you, do not speed up. Increase your own gap ahead so you can brake gently, and let them pass when it is safe.
• At night, do not sit on the tail lights of the car in front. It draws you in too close.

Common mistakes

• Judging the gap by eye. Count the seconds.
• Keeping a dry-weather gap in the rain. Double it.
• Closing up in slow traffic. Leave room to stop and to steer round if the car in front stalls.
• Braking hard when someone cuts in. Ease off gradually instead.
• Speeding up when tailgated. Keep a safe speed and let them pass.

Test yourself: Following distance

Answer each question, then read the explanation. Questions come in a random order each time.

Go deeper

• Two Second Rule and Stopping Distances in Ireland