Final answer:
The two most frequent causes of motorcycle accidents are driver error and head or traumatic brain injuries.
Step-by-step explanation:
The two most frequent causes of motorcycle accidents are driver error and issues related to the skeletal system, such as head and traumatic brain injuries. Driver error, including factors like speeding, lack of experience, or distracted driving, accounts for a significant proportion of accidents. Head and traumatic brain injuries can have immediate and severe consequences, either due to the accident itself or subsequent complications like bleeding or infections. According to the American Automobile Association, driver error is responsible for approximately 54 percent of all fatal auto accidents. Brain injuries are also a major cause of injury-related deaths, with falls, automobile, and motorcycle accidents as leading causes.