Police Lt. Mark Kotte says officers stopped Shepard early Saturday in the central Illinois town of Normal.
Kotte says the 65-year-old Shepard was driving 16 mph over the 30 mph speed limit.
Kotte says a breath test indicated Shepard's blood-alcohol level was double the legal limit.
Shepard told police he had been at a tavern in nearby Bloomington and was heading to a hotel. He said he was on his way to his home in Kentucky from Minnesota.
Shepard won the 1979 Pulitzer Prize for drama for his play "Buried Child."
He posted bail in Bloomington. A man who answered the jail phone said he did not know the amount of bail.
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