From Wazeopedia
Category U-turn-prevented.png       Prevent U-turn
(all must be present)
U-turn-permitted.png         Enable U-turn
(any must be present)
Segment count Must be 3 segments Any segment count other than 3
Median length Must be 45.93 ft (14 m) or less Must be 52.49 ft (16 m) or more
In-out Parallelism Must be between 175° and 185° Must be less than 175° or greater than 185°