Core: 3-second rule: greater following distance in rain, snow, fog and heavy loads

The book names five situations in which you extend the ordinary 2-second rule to 3 seconds: rain, snow, fog, a heavily loaded vehicle, and a trailer or caravan (Book p.124). In each of these cases your grip is lower or your braking distance longer than normal — the extra second compensates for that. Three seconds is 1.5 times as much as two, not a doubling to four. Anyone who takes 'double your distance' literally keeps too much distance and can end up being cut off or overtaken awkwardly on a busy road. The cause of many rear-end collisions on motorways is exactly this: too tight a following distance, combined with distraction or fatigue (Book p.124). The 3-second rule in difficult conditions is the direct countermeasure.