Kennedy is the daughter of Sen. Robert F. Kennedy and niece of President John F. Kennedy.
Police say she was arrested Friday after her car struck a tractor-trailer on an interstate north of New York City and she took an exit off it. They say an investigation found she was impaired by drugs.
A spokesman for Kennedy says breath, blood and urine tests revealed no drugs or alcohol in her system. Her lawyer says she'll plead not guilty Tuesday night.
Kennedy's sister-in-law Mary Kennedy hanged herself in May. Her brother Douglas Kennedy is fighting charges stemming from his attempt to take his newborn son from a maternity ward.