Distances and numbers
The distance rules for the exam, each with a model you can drag to see how it behaves at different speeds.
Stopping distance is not linear
Three formulas, all built on one input: your speed divided by ten. These are the standard German driving-school rules of thumb — the exam expects you to calculate with them, and they are close enough to physics to trust.
Reaction distance — how far you travel in the roughly one second before your foot even reaches the brake: (speed ÷ 10) × 3. At 50 km/h that is 15 m; at 100 km/h, 30 m. Linear: double the speed, double the distance.
Braking distance — how far the car travels once braking normally: (speed ÷ 10)². At 50 km/h, 25 m; at 100 km/h, 100 m. This one is squared, and the square is the whole lesson: doubling your speed quadruples the braking distance. Speed limits are set by this curve, not by cruelty.
Emergency braking (Gefahrbremsung — full-force stop): half the normal braking distance, so (speed ÷ 10)² ÷ 2. At 100 km/h: 50 m of braking, plus the unchanged 30 m of reaction — 80 m in total. Note what emergency braking cannot fix: the reaction distance. No brake shortens the second in which you have not yet reacted; only lower speed does.
Stopping distance is always reaction plus braking. At 100 km/h: 30 + 100 = 130 m under normal braking — well over a football pitch. Drag the slider and watch which component grows faster.
100 km/h
At 100 km/h you need 130 m to stop. Doubling your speed does not double it: braking distance alone goes up four times.
§ 3 Abs. 1 StVO · § 4 Abs. 1 StVO
Drive within what you can see
§ 3 Abs. 1 StVO contains the rule that generates half the numbers in this track: you may only drive so fast that you can stop within the stretch of road you can actually see (Sichtfahrgebot — the sight-distance rule). Fog, night, a crest, a curve: whatever shortens your sight line shortens your permitted speed, automatically, without any sign saying so.
Set the slider to your speed and compare the stopping distance against a sight line. At 100 km/h you need 130 m; if the fog gives you 60 m, the law has already lowered your limit for you — no sign required.
Two sharpened versions of the same idea:
On a road too narrow for two vehicles to pass — think country lanes with blind crests — you must be able to stop within HALF your sight distance, because whatever appears in front of you may be moving towards you and needs the other half to stop in (§ 3 Abs. 1 StVO).
When fog, snowfall or rain cut visibility below 50 m, the ceiling becomes concrete: no faster than 50 km/h, everywhere, unless a lower limit applies anyway (§ 3 Abs. 1 StVO). The 50 m are readable off the guide posts on rural roads — one post interval. The same threshold gates the rear fog light (Nebelschlussleuchte): it may only be switched on when fog cuts visibility below 50 m, and with it on you are capped at 50 km/h (§ 17 Abs. 3 StVO). The pairing is deliberate — the lamp that saves you from being rear-ended in fog dazzles everyone behind you in anything less.
100 km/h
At 100 km/h you need 130 m to stop. Doubling your speed does not double it: braking distance alone goes up four times.
§ 3 Abs. 1 StVO · § 17 Abs. 3 StVO
Half the speedometer
§ 4 Abs. 1 StVO states the principle without a number: the gap to the vehicle in front must generally be large enough that you can stop even if it brakes suddenly. German driver training turns that into numbers you can hold while driving, and the exam tests the numbers.
Outside built-up areas: half your speedometer reading, in metres. At 80 km/h keep about 40 m; at 100 km/h, about 50 m; at 130 km/h, about 65 m. Read it off the road with the guide posts (Leitpfosten), which stand 50 m apart on rural roads.
Inside built-up areas the half-speedo gap would be absurdly long for stop-and-go traffic, so the working rule is the distance you cover in about one second — at 50 km/h roughly 15 m, about three car lengths.
Why half, and not the full stopping distance? Because the car ahead of you cannot stop instantly either — it has its own braking distance, and yours nests inside it. Half the speedometer buys you back the piece that is truly yours alone: your reaction time. Which is also why the rule fails if you are tailgating something that CAN stop almost instantly — a car hitting a wall or a lorry hitting the car ahead.
One codified special case: trucks over 3.5 t and buses on the Autobahn must keep at least 50 m whenever driving faster than 50 km/h (§ 4 Abs. 3 StVO) — one full guide-post interval, fixed, not speed-scaled.
100 km/h
At 100 km/h you need 130 m to stop. Doubling your speed does not double it: braking distance alone goes up four times.
§ 4 Abs. 1 StVO · § 4 Abs. 3 StVO