How many times will the braking distance lengthen if you double the speed of the bus that you are driving?
Show the correct answer
Correct answer
B. Four times.
Explanation
In the photo you can see an intercity bus driving along a street. When you double the speed of the bus, its braking distance becomes four times longer - answer B.
The Road Traffic Act requires you to drive at a speed that ensures control of the vehicle and to keep a following distance that allows you to avoid a collision if the vehicle in front brakes. The braking distance grows with the square of speed, because the energy of motion, which the brakes must turn into heat, grows in the same way: twice as fast means a four times longer distance, and three times as fast - a nine times longer one. Answer A assumes a simple proportion, and answer C overstates the result. In a bus with passengers this is particularly important, because you cannot brake very hard without the risk that standing passengers will fall over. On top of the braking distance there is also the distance travelled during your reaction time.
Legal basis: Art. 19 para. 1 and para. 2 point 3 of the Road Traffic Act (Prawo o ruchu drogowym)