Speed, stopping distance and safe following
Speed, stopping distance and safe following are tested through scenario calculations and judgement questions. The exam wants you to connect speed with reaction time, braking distance and the space you need to see and stop.
The distance chain
Stopping distance is reaction distance plus braking distance. Reaction distance grows linearly with speed: at 80 km/h, one second covers about 22 metres. Braking distance grows much faster because kinetic energy rises with the square of speed. Wet, icy or gravel surfaces reduce grip and extend braking.
Following and limits
Use at least a two-second gap in good dry conditions; double it in rain and increase much more on ice or in poor visibility. A posted limit is a maximum for ideal conditions. Slow down for junctions, crests, blind bends, roadworks, pedestrians and heavy rain.
Worked example
At 80 km/h you leave a two-second gap, about 44 metres. The road becomes wet, so you increase the gap to four seconds, about 88 metres. If the car ahead brakes suddenly, your extra distance buys reaction and braking time. You also reduce speed to 60 km/h because the spray is reducing visibility.
Traps
Do not count only the car length ahead; gaps are time-based. Do not assume ABS shortens stopping distance on ice-it mainly helps steering control. Do not use the speed limit as proof that the speed is safe. In winter, braking distance can be several times longer than on dry asphalt.