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{{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.
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 involves is a reversal of driving direction through 3 three segments: <br>A) an incoming segment&nbsp;(A), B) a single median segment, &nbsp;(B) and C) an outgoing segment&nbsp;(C).# Segment '''Short median''': The median segment&nbsp;(B ) is shorter than 15 m meters (49.21 feet)or shorter.# Segment '''In/out parallelism''': The in and out segments (A &nbsp;and segment B &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 a 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 the median segment &nbsp;(B longer than 15 m ) 16 meters (4952.21 ft5 feet)or ''longer''* To allow a U-turn from only one direction, first set up U-turn prevention for both directions. Then, to allow Break condition #3 on the side where U-turns on one side, change are allowed. Increase or decrease the angles for segment so that the in and out segments (A and segment B so they 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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==== {{@|Checking for parallel incoming and outgoing segments}} ====
Condition #3 for U-turn prevention requires that the incoming in and outgoing out segments to be (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 the angles. JAI may be set for absolute or [[How_Waze_determines_turn_/_keep_/_exit_maneuvers|turn angles]]; using either setting is OK.
===== {{@|Straight median segments}} =====If the median segment &nbsp;(B ) is straight, measure add the angles angle between the in-segment &nbsp;(A ) and segment median&nbsp;(B, ) and the angle between segment the median&nbsp;(B ) and out-segment &nbsp;(C). If the sum of these angles is {{font color|red|between 175º and 185º}}, segment the in and out segments (A &nbsp;and segment B &nbsp;C) are considered parallel.
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[[File:U-turn_Parallel_Check_Straight.png||center680px]] ===== {{@|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.
If segment B has geometry nodes it is not straight. It cannot be used to measure ''Note: Be sure the turn angles. Insteadjunctions are unlocked, draw otherwise connecting a straight temporary segment to the same locked junctions used by segment B. Check the angles using this straight medianwill give a save error even if it is deleted prior to saving. Delete the straight median afterwards''
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[[File:U-turn_Parallel_Check_Curved.png||680px]]
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==== {{@|Common mistakesAdditional 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>
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