Each Limit, Translated Into Metres

Numbers on signs are abstract; the stopping table from the previous lesson makes them physical. Dry figures, with wet-season in brackets:

• 30 km/h — stop in ~18 m (22 m). Four to five car lengths. Short enough to stop within a school gate's sightlines — which is the entire point, and the next sub-topic's whole subject.
• 50 km/h — ~34 m (46 m). The urban limit: roughly a city junction plus its approach. Anything faster in town means the routine surprises — the opening car door, the crossing pedestrian, the reversing vehicle — arrive inside your stopping distance instead of beyond it.
• 80 km/h — ~65 m (97 m). The lorry and expressway tier. The wet figure is a full football pitch — and heavy vehicles' braking systems and loads stretch it further still, which is exactly why 80 is their ceiling.
• 100 km/h — ~92 m (142 m). Open rural roads — the very roads shared with livestock, crossings and non-motorised traffic. The limit assumes long sightlines; where the sightlines aren't long, the limit isn't the target.
• 110 km/h — ~107 m (167 m). Dual carriageways only — the one environment engineered to remove the surprises the other limits budget for: no oncoming stream, no same-level crossings, controlled access.

The pattern worth internalising: each limit is roughly the highest speed from which a driver can stop within the surprise-distance that road type generates. Change the surprise distance — rain, night, a school gate — and the appropriate speed changes with it, the sign unchanged.