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Routing penalties/Controlling U-turn penalties

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Median U-turn penalty link to this section

For the latest discussion on this section please visit the wiki forum thread.
U-turn Roads.png

The Waze routing algorithm assesses a penalty for a double-left or double-right turn, which can be used to prevent U-turns at H-style intersections on divided and parallel roads.

Preventing median U-turns link to this section

A large U-turn penalty is applied for a double-left or double-right turn when all three of the conditions below are met:

  1. The U-turn involves a reversal of driving direction through 3 segments:
    an incoming segment, a single median segment, and an outgoing segment
  2. The length of the median segment is shorter than 15 m (49.21 feet)
  3. The incoming and outgoing segments are within ±5° of parallel to each other


It is possible for this method to fail to prevent a U-turn when it is the first segment of a route or reroute. If you observe this method to fail when it is implemented properly, please report it in this forum thread


Allowing median U-turns link to this section

To allow a double-left or double-right turn through a median segment, break any one of the above criteria. For example:

  • To allow median U-turns in both directions, break condition #2 by making the median segment longer than 15 m (49.21 ft)
  • To selectively allow a U-turn from only one direction, first setup U-turn prevention as you would for both directions. For the side where U-turns are allowed, make the incoming and outgoing segments sufficiently non-parallel. (Tip: consider using a Micro-dogleg to discreetly tweak the angle without affecting appearance)


Checking for parallel incoming and outgoing segments link to this section

Condition #3 for U-turn prevention requires the incoming and outgoing segments to be within ±5º of parallel to each other. These two segments are considered parallel if their angles with respect to a straight median segment sum to 180±5º (i.e, between 175º and 185º).

Angles can be easily checked with the Junction Angle Info script add-on, which can be set to report absolute angles or turn angles ("departure"). For the purpose of determining parallelism, summing either measurements will work.

U-turn Parallel Check Straight.png


However, if the median segment has geometry nodes and is not straight, it cannot be used as a reference. In this case, temporarily add a straight segment to the same junctions as the existing curved median. Check the angles using this straight median and delete when done.
U-turn Parallel Check Curved.png

Common mistakes link to this section