Question Emergency brakes: Answers Are not required on trucks. Are only required on trailers. Are required on tractors. Are optional. Explanation All trucks, truck tractors, and buses must be equipped with emergency brakes and parking brakes. These brakes must be held by mechanical force. Take a FREE Practice Test Now This questions appears in the following tests: Arkansas Knowledge Test Class B , Georgia Knowledge Test Class B , District Of Columbia Air Brakes , Illinois Air Brakes , New Jersey Air Brakes , New York Air Brakes , North Dakota Air Brakes , Wisconsin Air Brakes ,