the driver reduces engine braking by shifting back up, or disengaging the clutch on a manual transmission, traction can be regained. In hybrid electric vehicles, like the Toyota Prius, engine braking is simulated by the computer software to match the feel of a traditional automatic transmission. For long downhill runs, the "B" mode acts like a lower gear, using the higher RPM of the internal combustion engine to waste energy, preventing the battery from being overcharged. Almost all electric and hybrid vehicles are able to convert kinetic motion into electricity, i.e. regenerative brakes, but since the internal combustion engine is not used to slow the vehicle when using regenerative braking, it is not the same as engine braking. Limitations Engine braking is a generally accepted practice and can help save wear on friction brakes. It is even used in some motor sports to reduce the risk of the friction brakes overheating. Additionally, fuel injection engines generally do not use fuel while engine braking. This is known as deceleration fuel cut-off (DFCO). Although no longer in production in most countries, there are still plenty of carbureted engines in service, with which engine braking is counter-productive to fuel economy due to the lack of a DFCO mechanism. The cost of wasted fuel can well outweigh the gain of reduced brake wear. Compression-release ("Jake") braking, a form of engine braking used almost exclusively on diesel engines, produces extreme amounts of noise pollution if there is no muffler on the intake manifold of the engine. Anecdotally, it sounds similar to a jackhammer, however the loudness is between 10 and 20 times the sound pressure level of a jackhammer (10 to 13 dB greater). Numerous cities, municipalities, states, and provinces have banned the use of unmuffled compression brakes, which are typically only legal in roads away from populations. In Australia, traffic enforcement cameras are currently being tested that automatically photograph heavy vehicles that use compression braking. See also Dynamic braking, similar effect with electric engines Retarder Certain types of braking in steam locomotives that are conceptually comparable (using compression in the steam engine cylinders for braking) Countersteam brake Counter-pressure brake References Vehicle braking technologies Noise pollution Motorcycle dynamics