Safe driving, following distance and speed management
Safe driving, following distance and speed management
This domain tests whether you can choose a speed and a gap that match the vehicle's mass, the road and the conditions - the two decisions that most often decide whether a heavy vehicle crash happens.
Following distance
- Use the time gap, not metres. Pick a fixed object ahead; when the vehicle in front passes it, count seconds until you pass it.
- Three seconds is the minimum for a car in good conditions. A loaded combination needs at least four, and more with rain, sand, night, or a tailgater behind.
- Add roughly one second per adverse factor, and a further second if the road is wet or visibility is reduced by dust.
Speed management
- Highway limits top out near 120 km/h for light vehicles, but heavy trucks and buses are restricted to about 80 km/h and must have a functioning speed limiter. A limiter is a cap, not a target.
- Braking distance grows with the square of speed: going from 80 to 100 km/h does not add 25% to stopping distance, it adds around 56%, before reaction distance is counted.
- On downgrades, select the gear before the slope, not after the speed has built.
- Overtaking needs a gap you can complete in, plus a margin for the length of the combination; if in doubt, stay behind.
Worked example
At 80 km/h you travel 22.2 m every second. A four-second gap is about 89 m. If the truck ahead brakes hard, you still need reaction time (roughly 1–1.5 s, or 22–33 m) before the brakes bite, then the braking distance on top. Reasoning: the 89 m gap is consumed almost entirely by reaction plus the first part of braking, which is why a heavier vehicle needs a longer gap, not the same one held by the car behind.
Traps that cost marks
- Quoting a gap in vehicle lengths, which changes with the size of the vehicle ahead.
- Treating the speed limiter as permission to sit at the limit in dust or rain.
- Measuring the gap only when the road is empty and the load is light.