Joan Kennedy, the ex-wife of Sen. Edward Kennedy, was arrested on her third drunken driving violation since 1974, state police said Wednesday.

The arrest comes at a time when her former husband's family is mired in a rape scandal in Florida.Kennedy, 55, an admitted alcoholic, was arrested about 9:30 p.m. Tuesday on Route 3 in Quincy by state police who said they saw her car weaving across all three northbound lanes on the high-speed expressway south of Boston. Traffic had backed up behind her weaving auto, state police said.

Police said that when two cruisers approached her car, Kennedy stopped between the first and second lanes of the highway. They escorted her vehicle to the breakdown lane.

Kennedy reportedly took several field sobriety tests and was taken to Norwell State Police barracks but was later bailed out by friends, troopers said. There was no indication where she had been before the arrest.