The Table, and the Assumptions Under It

Every stopping table smuggles in assumptions; this one declares them first.

• Reaction time: 1.5 seconds. Mid-range of the normal 0.5–2s span — a realistic alert driver, not a startled one and not a racing driver. If a table elsewhere uses 1.0s, its reaction column will read shorter; neither is "wrong," they model different drivers.
• Dry tarmac: friction coefficient f = 0.8. Good tyres, good brakes, sound surface.
• Wet tarmac: f = 0.4 — half the dry grip, hence exactly double the dry braking distance. Real wet grip varies; 0.4 is a fair planning figure for steady rain on decent tarmac, and optimistic for the first rain after a dry spell.
• Flat road, functioning brakes on all wheels, sensible load. Gradient, defects, and overloading all extend the figures.

Now the table. All distances in metres, rounded. Reaction at 1.5s applies to both surface columns — rain doesn't slow your brain, only your tyres.

Reading the table's shape — three observations worth more than any single row:

1. Watch the two columns trade places. At 30 km/h, reaction distance dominates (13 vs 5). By 100 km/h, braking dominates (50 vs 42). Low-speed safety is mostly about alertness; high-speed safety is mostly about physics — which is why anticipation pays biggest in town and speed choice pays biggest on the highway.
2. Wet doubles the braking column, not the total — but the totals still balloon: at 110 km/h, rain adds 60 metres to your stop.
3. The quadratic signature is visible down the braking column: 30→110 km/h is under 4× the speed but over 12× the dry braking distance.

Landmarks, using a 4-metre car length:

• 50 km/h dry — 34 m: eight to nine car lengths. In town, that's often past the junction you were stopping for.
• 80 km/h wet — 97 m: the full length of a football pitch, plus a bit.
• 110 km/h wet — 167 m: more than one and a half pitches; roughly 12 matatu lengths of highway.