Question What is a retarder? Answers A device that prevents a vehicle from going too fast A device that prevents a vehicle from being too loud A device that improves a vehicle's gas mileage Explanation Retarders help to slow vehicles, reducing drivers' need to use brakes. Take a FREE Practice Test Now This questions appears in the following tests: Michigan Knowledge Test Class A , Nebraska Knowledge Test Class A , South Dakota Knowledge Test Class A , Iowa Double , Hawaii Tank , New Mexico Tank ,