How Engine Brakes Work

­Engine brakes are used when a semi driver is in stop-and-go traffic and when driving on downhill grades. They are also used on the following vehicles and equipment:

Like exhaust brakes, engine brakes should be used continuously -- not just when traversing a steep decline. This will help to reduce wear on the normal service brakes. And if you've ever needed your brakes replaced, you know that can cost a pretty penny.

­You can hear engine brakes in action while driving on a typical interstate or highway. Drivers regularly switch on the engine brakes to slow down. This creates the blatting sound that ricochets off any surrounding buildings or vehicles.

Engine brakes often get a bad rap due to the noise that is attributed to their use. When a semi uses engine brakes you will often hear a loud blat-blat-blat, sometimes referred to as a Jake Bark because the compressed air is forced through the exhaust valve in the engine's cylinder.

Jacobs Vehicle Systems, the leading manufacturer of engine brakes, says that the noise emitted by a properly maintained rig with an OEM muffler is within the 80 to 83 decibel dB(A) range, which is 10 to 13 decibels above the high range of normal conversation. Jacobs Vehicle System states the main reason for the loud staccato noise that often accompanies their use is improperly muffled vehicles. Straight stack exhaust systems have a sound level that is 16 to 22 decibels higher than properly muffled vehicles [source: Jacobs Vehicle Systems].

­­Legislation has been passed banning the use of engine brakes in some states, but changes are being made to address the root of the problem. Read on to learn the laws and possibly help to create your own.