Question Which of the following is not a type of retarder? Answers Exhaust Engine Air Electric Explanation Retarders are mechanisms in some vehicles that help slow a vehicle and reduce the need for braking. The four basic types of retarders are exhaust, engine, hydraulic, and electric. This questions appears in the following tests: Maryland Class A Knowledge Test Maryland Double New York Class B Knowledge Test North Dakota Class B Knowledge Test North Dakota Class B Knowledge Test Pennsylvania Class B Knowledge Test South Carolina Double Texas Passenger Utah Double