Elizabeth Dazzio was driving her sister and a friend home from the singer's show in Louisiana when she fell asleep at the wheel.
Dazzio was knocked unconscious when the car crashed.
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The other two girls were trapped, unable to reach their phones, and fearful that no one would see them off the side of a highway.
So to signal help, they held up flashing bracelets they had bought during Swift's concert.
Eventually a woman saw the blinking lights and called 911.
All of the girls are expected to make a full recovery.