Two-way segments will also show the small U-turn arrow icon at both ends of the segment. This is used, as its name suggests, to prevent/enable Waze to use a segment end node as a U-turn, in case of necessity.
The standard rule in the BeLux: U-turns should be disabled: 
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U-turns explained
A curved green arrow indicates that a u-turn is allowed in the manner and direction indicated by the arrow at that end of the segment.
When you hover the mouse over an allowed u-turn arrow, a small clock icon appears, which, when clicked on, allowed you to set scheduled u-turn restrictions, as well as vehicle type restrictions on the U-turn.
A curved red arrow with the slashed-circle icon indicates that a u-turn is not allowed (is restricted) in the manner and direction indicated by the arrow at that end of the segment.
A curved yellow arrow with a clock icon indicates the presence of scheduled (time-based) turn restrictions for the direction indicated by the arrow at that end of the segment.
When can U-turns be used
There are some exceptions on the rule that "In the BeLux: U-turns should be disabled"
If a unpenalized route ends on a penalized route
We know that waze want to continue a new route in the direction you arrived at a previous destination. If this lead to a penalized route than Waze try to find a way out over this penalized segments. To avoid this we can add a U-turn on transitions to this penalized segments:
- Parking Lot Road
- Private road
- 4x4 road (off-road)
- unpaved road
- Narrow street
The U-turn is not needed on transition to Walking Trail or Pedestrian Boardwalk. The error message on this junctions may be ignored.
On roads where both directions are separated by a shoulder or a continuous white linea
To reach the correct destination a U-turn (if allowed) may be necessary
Remarks
- See for U-turn prevention the Road aspects page paragraph Double left and double right.