In which of the following cases do you get the most effective braking in a bus with a retarder?
Show the correct answer
Correct answer
B. At high engine revolutions.
Explanation
In the photo you can see the driver's position in a bus with the steering wheel, pedals and switches. You get the most effective braking with the exhaust brake (engine brake) at high engine revs - answer B.
The Road Traffic Act requires you to drive at a speed that ensures control of the vehicle and to brake safely. The engine brake restricts the exhaust outlet or changes the operation of the valves, so the engine resists the wheels - the higher the revs, the greater this resistance. That is why before a descent you shift down, so that the revs are high but do not go into the red area. At low revs (answer A) the engine brake works weakly. Low speed of the bus (answer C) does not in itself increase its effectiveness - what counts is the revs in the given gear. At low speed, the engine brake often switches off completely.
Legal basis: Art. 19 para. 1 and para. 2 point 2 of the Road Traffic Act (Prawo o ruchu drogowym)