Routing penalties/Controlling U-turn penalties: Difference between revisions View history

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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}}
{{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].}}
{{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]}}
 
[[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.
 
 
==== {{@|Preventing median U-turns}} ====
 
U-turns via a median segment are heavily [[Routing penalties|penalized]] when all three of the conditions below are met. This prevents U-turns at box- (#) and H-style intersections on divided highways and parallel roads.
 
# The forbidden U-turn is composed of one incoming segment, one median segment, and one outgoing segment.
# The length of the median segment is shorter than 15 m (49 feet).
# The portion of those two segments closest to the median segment must be [[#Checking for parallel segments|within ±5° of exactly parallel]].
 
==== {{@|Allowing median U-turns}} ====
 
To allow a U-turn through a median, ensure that any one of the [[#Preventing median U-turns|above criteria]] are broken:
 
* To allow the median U-turn in both directions, it is simplest to make the median segment longer than 15 meters. ''(Breaking condition #2)''
* 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]].
 
==== {{@|Checking for parallel segments}} ====
 
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.''
 
Check two angles:
# X — the angle between the incoming one-way segment and the reference segment
# Y — the angle between the outgoing one-way segment and the reference segment.
 
If the sum of these two angles is within 5° of 180° (between 175-185°), then the roads are considered parallel.
 
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.
[[File:LilyPondU-turn.jpeg]]

Latest revision as of 18:18, 8 January 2022

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