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| === {{@|Median U-turn penalty}} ===
| | #REDIRECT [[USA:Routing penalties/Controlling U-turn penalties]] |
| {{anchor|Avoiding U turns|Avoiding U turns in box and partial box intersections}}
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| {{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].}}
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| {{Mbox|type=important|text=It is possible for this method to fail to prevent U-turns when the uturn 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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| [[File:MinSegLengthUturn2.png|border|390px|right|Segment too short to allow two left turns]] | |
| The Waze routing algorithm assesses a [[Routing penalties#Road_configurations|penalty]] for a double-left turn in [[right-hand traffic]] countries and a double-right in [[left-hand traffic]] countries.
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| ==== {{@|Preventing median U-turns}} ====
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| U-turns through a median segment will be [[Routing penalties|penalized]] when all three of the below criteria are met. This allows the prevention of U-turns on divided highways, parallel roads, including box (#), and H style intersections.
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| # The U-turn we want to forbid is one incoming one-way segment, one median segment, and one outgoing one-way segment.
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| # There is a median segment of length less than 15 m (49 feet).
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| # The portion of those two segments closest to the median segment must be [[#Checking for parallel segments|within ±5° of exactly parallel]].
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| ==== {{@|Allowing median U-turns}} ====
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| To allow a U-turn through a median, ensure that any one of the [[#Preventing median U-turns|above criteria]] are broken:
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| * To allow the median U-turn in both directions, it is simplest to make the median segment longer than 15 meters. ''(Breaking criteria #2)''
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| * To allow the U-turn in only one direction, it is simplest to adjust the turn angles in only for the segments of the allowed U-turn so they are wider than the [[#Checking for parallel segments|±5° allowance of exactly parallel]]. This is easily achieved without affecting the overall look of the map using a [[Glossary#mDL|Micro-dogleg]].
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| ==== {{@|Checking for parallel segments}} ====
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| A convenient way to check if the two side segments are parallel is to use another segment as a reference tool. If the median segment has no geometry nodes, it can be the reference segment. Otherwise you can draw a new segment as a reference tool with no geometry which connects the A and B nodes of the median segment. ''The reference segment can be deleted after the check is complete, if appropriate.''
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| Check two angles:
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| # X — the angle between the incoming one-way segment and the reference segment
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| # Y — the angle between the outgoing one-way segment and the reference segment.
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| If the sum of these two angles is within 5° of 180° (between 175-185°), then the roads are considered parallel.
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| In the example below, angle X is 102°, and angle Y is 75°. The sum is 177°, which is within 3° of 180°. Therefore these roads are considered parallel.
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| [[File:LilyPondU-turn.jpeg]]
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