# Difference between revisions of "Routing penalties/Controlling U-turn penalties"

 Bring up comments or questions on this section in  [Page Update] Intersections / U-turns under 15m.
 Note: The road types displayed in the images might not match the standards for where you edit. Please check your local wiki and with local experts to learn the correct road type to use for median segments in your area.

The Waze routing algorithm has a method of penalizing some double-left and double-right turns. This can prevent U-turns at H or # style intersections on divided and parallel roads.

It is useful for preventing the sequence of two turns that would make up the U-turn, while still allowing the individual turns. However, if either of the two turns making up the U-turn is illegal or impossible, disallow that turn instead. The U-turn will then not be routed, and the following penalty does not matter.

#### Preventing median U-turns

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

1. Three segments: The U-turn is a reversal of driving direction through three segments:
an incoming segment (A), a single median segment (B) and an outgoing segment (C).
2. Short median: The median segment (B) is equal to 45.93 ft (14 m) or less.
3. In/out parallelism: The in and out segments (A and C) 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 it immediately follows a reroute. If you observe this method to fail in other situations when it is implemented properly, please report it in this forum thread

#### Allowing median U-turns

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To allow median U-turns in both directions, break condition #2 by making the median segment (B) 52.49 ft (16 m) or longer

To allow a U-turn from only one direction, first setup the intersection to allow U-turns in both directions. Then, add a Junction Box, and restrict the prohibited U-turn route. A rank 4 user or above is required to install a Junction Box.

 Previously, unidirectional U-turn prohibition on a divided road was set up by breaking condition #3 of the U-turn prevention mechanism through the use of a micro-dogleg. As of 2017, Waze staff has expressed a preference that map editors use Junction Boxes in these situations.

#### Checking for parallel incoming and outgoing segments

Condition #3 for U-turn prevention requires that the in and out segments (A and C) are within ±5º of parallel to each other. This is checked by using a straight median segment as the reference and the Junction Angle Info (JAI) browser extension to measure angles. JAI may be set for absolute or turn angles; using either is OK.

##### Straight median segments

If the median segment is straight, sum the two angles making up the U-turn:

1. The angle between the incoming and median segments (between A and B)
2. The angle between the median and outgoing segments (between B and C)

The in and out segments (A and C) are considered parallel if the sum is between 175º and 185º.

 The short 14m median segment in the above examples satisfies condition #2 for U-turn prevention.
##### Curved median segments

If the median segment (B) has been shaped with geometry nodes, it is not straight and cannot be used for determining parallelism. Instead, draw a straight segment connected at the same in and out junctions (where in-segment (A) junctions with the median segment (B) and where the median segment (B) junctions with the out-segment (C)). Check the angles using this new straight segment, and delete the new segment afterwards.

 Be sure the junctions are not locked above your rank. Otherwise, drawing a new temporary segment connected to locked junctions may produce a save error even if it is deleted prior to saving. Click Expand for details on workaround options when any segments connected to either junction node cannot be edited. Disable the WME setting "Draw new roads with all turns allowed" before drawing the new segment. Draw the new segment disconnected from any other segment, then drag the end nodes to connect to the junctions.