Approximately, by how much does the braking distance increase if speed is doubled?
Show the correct answer
Correct answer
A. Four times.
Explanation
In the photo you can see the rear of a tractor on wet asphalt with fallen leaves. When the speed is doubled, the braking distance increases approximately four times - answer A.
The energy of motion, which the brakes must turn into heat, grows with the square of the speed. Twice as fast means four times as much energy, so with the same braking force you need a section of road roughly four times longer to stop. Three times (answer B) and twice (answer C) are values that are too low - a driver who thinks this starts braking too late. On top of the braking distance there is also the distance travelled during the reaction time, which grows in proportion to the speed. On a wet surface with leaves, as in the photo, the braking distance itself is even longer. That is why even a small increase in the speed of a tractor with a heavy trailer clearly makes the stopping distance longer.
Legal basis: Art. 19 para. 1 of the Road Traffic Act (Prawo o ruchu drogowym)