Where are engine brakes used?

• Semitrailers
  Engine brakes are used in heavy duty and commercial vehicles -- like semitrailers and buses -- to increase speed control. How Engine Brakes Work
• Buses
  Engine brakes are used in heavy duty and commercial vehicles -- like semitrailers and buses -- to increase speed control. How Engine Brakes Work
• All of the above
  Engine brakes are used in heavy duty and commercial vehicles -- like semitrailers and buses -- to increase speed control. How Engine Brakes Work