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=== {{@|Median U-turn penalty}} ===
{{anchor|Avoiding U turns|Avoiding U turns in box and partial box intersections}}
{{Mbox|type=forum|text=For the latest discussion on this section please visit [http://www.waze.com/forum/viewtopic.php?t=108731 the wiki forum thread].}}
[[File:U-turn_Roads.png||360px|right]]
The Waze routing algorithm sets a [[Routing penalties#Road_configurations|penalty]] for some double-left or double-right turns. This can prevent U-turns at H-style intersections on divided and parallel roads.

==== {{@|Preventing median U-turns}} ====
A large U-turn penalty is set for a double-left or double-right turn when '''''all three''''' of the conditions below are met: 

# '''Three segments''': The U-turn is a reversal of driving direction through three segments: <br>an incoming segment&nbsp;(A), a single median segment&nbsp;(B) and an outgoing segment&nbsp;(C).
# '''Short median''': The median segment&nbsp;(B) is shorter than 15 meters (49.21 feet) or shorter.
# '''In/out parallelism''': The in and out segments (A&nbsp;and&nbsp;C) are  [[#Checking for parallel segments|within ±5° of parallel]] to each other
<br>{{Mbox|type=important|text=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 [http://www.waze.com/forum/viewtopic.php?p=994385#p994385 this forum thread]}}
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==== {{@|Allowing median U-turns}} ====

To allow a double-left or double-right turn through the median segment, break any one of the [[#Preventing median U-turns|above conditions]]. For example:

* To allow median U-turns in both directions, break condition #2 by making the median segment&nbsp;(B) 16 meters (52.5 feet) or ''longer''
* To allow a U-turn from only one direction, first set up U-turn prevention for both directions. Break condition #3 on the side where U-turns are allowed. Increase or decrease the angles so that the in and out segments (A and C) are [[#Checking for parallel segments|not parallel]]. A [[Glossary#mDL|micro-dogleg]] can be used to change the angle without changing the appearance of segment.
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[[File:U-turn selective Uturn prevention.png|center]]
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==== {{@|Checking for parallel incoming and outgoing segments}} ====

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

===== {{@|Straight median segments}} =====
If the median segment&nbsp;(B) is straight, add the angle between the in-segment&nbsp;(A) and median&nbsp;(B) and the angle between the median&nbsp;(B) and out-segment&nbsp;(C). If the sum of these angles is {{font color|red|between 175º and 185º}}, the in and out segments (A&nbsp;and&nbsp;C) are considered parallel.
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[[File:U-turn_Parallel_Check_Straight.png||680px]]

===== {{@|Curved median segments}} =====
If the median segment&nbsp;(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&nbsp;(A) junctions with median&nbsp;(B) and median&nbsp;(B) junctions with out-segment&nbsp;(C)). Check the angles using this straight segment and delete the segment afterwards. 

''Note: Be sure the junctions are unlocked, otherwise connecting a temporary segment to locked junctions will give a save error even if it is deleted prior to saving.''
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[[File:U-turn_Parallel_Check_Curved.png||680px]]
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==== {{@|Additional examples}} ====
<div style="font-size:smaller">
{| class="wikitable" cellpadding=2 style="width: 100%; text-align: left;" 
! style="width: 247px" | Example
! style="width: 120px" | Tip
!  Details
|- style="background-color: #fff;"
| [[File:U-turn_example_2mediansegs-bdp.png|243px]]
| Cutting a median segment into two may have unintended consequences
| U-turns are legal at this intersection. While U-turn prevention is ''not'' triggered here, Waze will rarely route a U-turn at this intersection. When the railroad was junctioned with the median segment, it cut a single median into two. The two segment discontinuity between divided roads of Major Blvd will trigger a lower penalty mechanism designed to discourage detours off the main road([[Detour_Prevention_Mechanisms/USA#Big_Detours|Big Detour Prevention]], BDP). 
|- style="background-color: #fff;"
| [[File:U-turn_example_2mediansegs-allowed.png|243px]]
| Cutting a median segment into two may have unintended consequences
| U-turns are not legal at this intersection, but Waze may route a U-turn here anyway. Cutting the median breaks condition #1, so U-turn prevention will not trigger. Unlike the railroad example, BDP will not trigger here, since the divided east and westbound roads do not have matching primary nor alternate names.
|- style="background-color: #fff;"
| [[File:U-turn_example_curvedU.png|243px]]
| A median segment longer than 15 m (49.21 ft) will always allow a U-turn
| While condition #3 requires a straight segment for determining parallel in and out segments, condition #2 is the measure of the length of the median segment itself. Be careful when the space between divided roads is small. Ensure the U-turn segment is longer than 15 m (49.21 ft) by adjusting its geometry. Conversely, a median segment of any shape can trigger a U-turn penalty if it is not long enough.
|- style="background-color: #fff;"
| [[File:U-turn_example_parkinglot.png|243px]]
| To ensure proper routing between two closely spaced parallel roads, connect the two with a segment longer than 15 m (52.5 ft)
| U-turn prevention triggers for both double-left and double-right turns over any road type. If the three conditions for median U-turn prevention are met, a large penalty will be applied, irrespective of whether the turn is onto the same road in the opposite direction or onto a completely different road. Both double-left and double-right turns can be penalized, regardless of country, and can occur on one way or two way segments.
|}
</div>