What a Hazard Is

A hazard is anything that may make you change your speed, your position or your direction. The definition is deliberately wide. It doesn't need to be dangerous yet, and it doesn't need to be in your path yet. A pedestrian waiting at the kerb is a hazard. So is a junction ahead, a parked matatu, a bend you can't see round, and a lorry shedding gravel. None of them may come to anything, but each one could ask you to do something.

The handbook draws the same line in its own words. It separates potential hazards, things that could become a problem, from actual hazards, the ones that already have. A potential hazard needs watching so that it never becomes an actual one. That is the whole skill of hazard perception: dealing with hazards while they are still potential.

Why it matters comes straight from The Physics of Stopping. Your stopping distance has two parts, reaction and braking. Braking is set by speed and grip, and you can't argue with it. Reaction distance is the part you can shrink, and the handbook's opening point is that most crashes are caused by human error. The Swedish Theory Book lists what shortens reaction distance: anticipation and preparedness. A driver who has already noticed the pedestrian, eased off and covered the brake doesn't need a full reaction time when the pedestrian steps out. They are already half-way through responding.

So hazard perception isn't a separate talent from safe driving. It is where the time comes from. You cannot brake sooner than you see.