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| === {{@|Controlling U-turns}} ===
| | #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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| [[File:U-turn_Roads.png||360px|right]]
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| 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 or # style intersections on divided and parallel roads which must be restricted, but both of the turns that make up that U-turn are individually allowed.
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| If one of the two turns making up the U-turn is restricted or impossible, disallow that turn. The U-turn will then not be routed, and the following penalty is not needed.
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| ==== {{@|Preventing median U-turns}} ====
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| 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:
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| # '''Three segments''': The U-turn is a reversal of driving direction through three segments: <br>an incoming segment (A), a single median segment (B) and an outgoing segment (C).
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| # '''Short median''': The median segment (B) is shorter than {{:Routing_penalties/U-turn_minimum}}.<br>''As a safety margin, leave a 1 m buffer zone by using {{:Routing_penalties/U-turn_minimum|less}} or less.''
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| # '''In/out parallelism''': The in and out segments (A and C) are [[#Checking for parallel incoming and outgoing segments|within ±5° of parallel]] to each other.
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| <br>
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| {{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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| <br>
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| ==== {{@|Allowing median U-turns}} ====
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| 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:
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| * To allow median U-turns in both directions, break condition #2 by making the median segment (B) {{:Routing_penalties/U-turn_minimum|greater}} ''or longer''
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| * 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 incoming and outgoing 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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| <br>
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| ==== {{@|Checking for parallel incoming and outgoing segments}} ====
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| 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 [[Scripts#WME_Junction_Angle_info|Junction Angle Info]] (JAI) browser extension to measure angles. JAI may be set for absolute or [[Interactive_junction_instruction_algorithm#Turn_angle|turn angles]]; using either is OK.
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| ===== {{@|Straight median segments}} =====
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| If the median segment is straight, sum the two angles making up the U-turn:
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| :# The angle between the incoming and median segments (between A and B)
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| :# The angle between the median and outgoing segments (between B and C)
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| The in and out segments (A and C) are considered parallel if the sum is {{font color|red|between 175º and 185º}}.
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| <br>
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| {| style="border: 0px;text-align: center; line-height: 1; font-size: small;"
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| |-
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| | [[File:U-turn_Parallel_Check_Straight.png|680px]]
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| |-
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| | style="padding-bottom: 20px;" | The 14m median segment in the examples above satisfies condition #2 for U-turn prevention.
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| |}
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| ===== {{@|Curved median segments}} =====
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| 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.
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| <br>
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| [[File:U-turn_Parallel_Check_Curved.png||680px]]
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| <br>
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| {{mbox|type=protection|text=Be sure the [[Editing_permissions#Locked_junction|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.
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| {{Expand|
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| # Disable the [[Map_Editor_Interface_and_Controls#Settings_Tab|WME setting]] "Draw new roads with all turns allowed" before drawing the new segment.
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| # Draw the new segment disconnected from any other segment, then drag the end nodes to connect to the junctions.
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| |workaround options when segment(s) connected to either junction node are locked above your rank.
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| |nt=yes}}}}
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| <includeonly>Please see the [[Routing penalties/Controlling U-turns#Additional examples|Controlling U-turns]] article for more advanced details, and additional examples.</includeonly><noinclude>
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| ==== {{@|Additional examples}} ====
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| <div style="font-size:smaller">
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| {| class="wikitable" cellpadding=2 style="width: 100%; text-align: left;"
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| ! style="width: 247px" | Example
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| ! style="width: 120px" | Tip
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| ! Details
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| |- style="background-color: #fff;"
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| | [[File:U-turn_example_2mediansegs-bdp.png|243px]]
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| | Cutting a median segment into two may have unintended consequences
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| | U-turns are legal at this intersection. Even though U-turn prevention will ''not'' be 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 can trigger a lower penalty mechanism designed to discourage detours off the main road (see [[Detour_Prevention_Mechanisms/USA#Big_Detours|Big Detour Prevention]], BDP).
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| |- style="background-color: #fff;"
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| | [[File:U-turn_example_2mediansegs-allowed.png|243px]]
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| | Cutting a median segment into two may have unintended consequences
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| | 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. Furthermore, BDP might not trigger here if all of its criteria are not met.
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| |- style="background-color: #fff;"
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| | [[File:U-turn_example_curvedU.png|243px]]
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| | A median segment longer than {{:Routing penalties/U-turn minimum}} will always allow a U-turn
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| | 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 the divided road is small. Ensure the U-turn segment is longer than {{:Routing penalties/U-turn minimum}} by adjusting geometry. A median segment of any shape can trigger a U-turn penalty between parallel roads if it is not long enough.
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| |- style="background-color: #fff;"
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| | [[File:U-turn_example_parkinglot.png|243px]]
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| | To ensure proper routing between two closely spaced parallel roads, connect the two with a segment {{:Routing penalties/U-turn minimum|greater}} or longer
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| | 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 for one way or two way segments.
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| |}
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| </div>
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| </noinclude>
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