Theory course · Topic 8 of 14
Topic 8
Speed
Speed is the one factor that magnifies every other mistake.
In short
Topic 8 does the arithmetic on what speed means when something goes wrong. The total stopping distance is the reaction distance you cover unbraked plus the braking distance, which grows with the square of the speed: double the speed, four times the braking distance. On top of that comes the most important sentence of the double lesson — permitted is not the same as appropriate. In rain, fog, darkness or dense traffic the posted limit is often far too fast.
Rule of thumb
The reaction distance grows with speed, the braking distance with the square of it. That is why the difference between 30 and 50 in a residential street is not a difference of twenty kilometres per hour, but the difference between stopping and hitting.
What this topic teaches you
The core is the rules of thumb. The reaction distance is speed divided by ten, times three — at 50 km/h that is around 15 metres covered before the brake even bites. The braking distance is speed divided by ten, times itself: about 25 metres at 50 km/h, but already 100 metres at 100 km/h. Together they make the total stopping distance, and that sum is why doubling your speed is not twice as dangerous but roughly three and a half times.
The second block is the obligation to drive within your sightline. You may only drive as fast as you can stop within the distance you can see — in fog, in darkness on dipped beam, beyond a crest, before a blind bend. A sign permitting 100 does not become wrong because of that; it simply stops being the answer to the question of how fast you may drive.
The third block is the fixed limits and their exceptions: 50 in built-up areas, 100 outside them for cars, 30 in zones, walking pace in traffic-calmed areas. Plus the rule with the greatest everyday effect: even with no sign at all, you are too fast when the situation leaves you no reserve.
- Reaction distance, braking distance, stopping distance
- Double the speed, four times the braking distance
- Driving within your sightline in fog and darkness
- Appropriate is not the same as permitted
What it looks like in Düsseldorf
Large parts of the residential quarters — Bilk, Flingern, Pempelfort, Derendorf — are 30 zones with priority to the right, cars parked on both sides and children between them. Thirty feels slow there and is not: out of a gap between two parked cars there is barely more than the reaction distance available. That is exactly why those streets are practised early in the training.
The counterpart is the motorway drives. On the A46 and the A52 speed limits, roadworks and traffic density change within a few kilometres, and there is regularly a queue at the junctions. Anyone with the stopping distance in mind keeps a gap there instead of looking for one once the brake lights come on ahead. On the Rhine bridges, crosswind is added, and at high speed it tugs noticeably at the steering.
What the test does with it
Topic 8 supplies the arithmetic questions in the theory test. You are asked for the reaction distance, the braking distance and the total stopping distance at a given speed, and occasionally for the halved braking distance of an emergency stop. The formulas are short, but they have to be solid — there is no calculator in the test room and no second run at thinking it through.
In the practical test it is less about exceeding limits than about speed that does not fit. Slowing too late before a bend, too small a gap to the car in front and holding your speed in a street you cannot see through are the usual notes. The reverse counts too: driving persistently well under the limit and obstructing traffic is marked as well.
- Knowing the rules of thumb by heart
- An emergency stop halves the braking distance
- Half the speedometer reading as a gap outside towns
- Neither too fast nor permanently too slow
Common questions
How do I calculate the total stopping distance?
Stopping distance is reaction distance plus braking distance. The reaction distance is speed divided by ten, times three. The braking distance is speed divided by ten, times itself. At 50 km/h that is about 15 metres plus 25 metres, so roughly 40 metres.
What does an emergency stop change?
In a full emergency stop the braking distance halves compared with normal braking. The reaction distance stays the same, because it happens before the braking. So 25 metres of braking distance at 50 km/h becomes around 12.5 metres.
How large a gap should I keep to the car in front?
Outside built-up areas the rule of thumb is half the speedometer reading in metres, so 50 metres at 100 km/h. In town a gap of roughly two seconds is usually enough. In rain, fog or darkness both get bigger, not smaller.
Does the speed limit apply on an empty road?
Yes, the permitted maximum is an upper limit and not a recommendation. But it is never a permission either: where visibility, weather or traffic demand it, you have to drive more slowly even though the sign allows more.