What is a “speed retarder”?

1. Correct answer: An electric or hydraulic mechanism, independent of the vehicle’s braking system, which decelerates the vehicle when operated.
2. An electronic system which automatically operates the brakes while driving on a steep decent, thus preventing brake overheating and brake loss.
3. A system installed in the vehicle that assists in emergency braking and stops the vehicle on the spot.
4. An electric mechanism installed in the braking system that shuts-off the engine and helps the vehicle to maintain constant speed on all roads.

WhyA speed retarder is an electric or hydraulic mechanism, separate from the brakes, that slows the vehicle when switched on. It spares the brakes on long descents.