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.
Why should U-turns be disabled
It causes unsafe, inconvenient, or unethical moves
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 then Waze tries to find a way out over this penalized segments. Or a user can accidentally enters a regular segment ending on a penalised segment? To avoid this we may 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.
Separated directions
On roads where both directions are separated by a shoulder or a continuous white line. To reach the correct destination a U-turn (if allowed) may be necessary
On large crossings with roads separated by a hard shoulder
If it is allowed, safe and convenient, then u-turns can be enabled on those crossings.
Traffic regulations
Sign D3 - D1
On this signs (D3, D1) only the displayed directions are allowed. In this case a u-turn is forbidden.
Road markings
- Art. 77.1. White pre-sort arrows may be displayed when approaching an intersection. These arrows indicate the lane that drivers must follow to drive in the direction indicated by the arrows.
- At the intersection, drivers must also follow one of the directions indicated in the lane in which they are located.
At an intersection with a hard shoulder, it is allowed to make a u-turn from the left lane with a left presort arrow, unless this is prohibited by traffic signs D3 or C33.
Remarks
- See for U-turn prevention the Road aspects page paragraph Double left and double right.