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Median U-turn penalty

For the latest discussion on this section please visit the wiki forum thread.

The Waze routing algorithm sets a 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:
an incoming segment (A), a single median segment (B) and an outgoing segment (C).
Short median: The median segment (B) is shorter than 15 meters (49.21 feet) or shorter.
In/out parallelism: The in and out segments (A and C) are within ±5° of parallel to each other

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 this forum thread

Allowing median U-turns

To allow a double-left or double-right turn through the median segment, break any one of the above conditions. For example:

To allow median U-turns in both directions, break condition #2 by making the median segment (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 not parallel. A micro-dogleg can be used to change the angle without changing the appearance of segment.

Checking for parallel incoming and outgoing segments

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 Junction Angle Info (JAI) browser extension to measure angles. JAI may be set for absolute or turn angles; using either is OK.

Straight median segments

If the median segment (B) is straight, add the angle between the in-segment (A) and median (B) and the angle between the median (B) and out-segment (C). If the sum of these angles is between 175º and 185º, the in and out segments (A and C) are considered parallel.

Curved median segments

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 median (B) and median (B) junctions with out-segment (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.

Additional examples

Example	Tip	Details
	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(Big Detour Prevention, BDP).
	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.
	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.
	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.

@@ Line 2: / Line 2: @@
 {{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.
@@ Line 9: / Line 8: @@
 A large U-turn penalty is set for a double-left or double-right turn when '''''all three''''' of the conditions below are met:
-# The U-turn involves a reversal of driving direction through 3 segments: <br>A) an incoming segment, B) a single median segment, and C) an outgoing segment
+# '''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).
-# Segment B is shorter than 15 m (49.21 feet)
+# '''Short median''': The median segment&nbsp;(B) is shorter than 15 meters (49.21 feet) or shorter.
-# Segment A and segment B are  [[#Checking for parallel segments|within ±5° of parallel]] to each other
+# '''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>
+<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]}}
-{{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]}}
 <br>
 ==== {{@|Allowing median U-turns}} ====
-To allow a double-left or double-right turn through a median segment, break any one of the [[#Preventing median U-turns|above conditions]]. For example:
+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 the median segment B longer than 15 m (49.21 ft)
+* 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. Then, to allow U-turns on one side, change the angles for segment A and segment B so they 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.
+* 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.
 <br>
 ==== {{@|Checking for parallel incoming and outgoing segments}} ====
-Condition #3 for U-turn prevention requires the incoming and outgoing segments to be within ±5º of parallel to each other. This is checked by using a ''straight'' median segment 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]]; either setting is OK.
+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.
-If segment B is straight, measure the angles between segment A and segment B, and between segment B segment C. If the sum of these angles is between 175º and 185º, segment A and segment B are considered parallel.
+===== {{@|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.
 <br>
-[[File:U-turn_Parallel_Check_Straight.png||center]]
+[[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.
-If segment B has geometry nodes it is not straight. It cannot be used to measure the turn angles. Instead, draw a straight segment to the same junctions used by segment B. Check the angles using this straight median. Delete the straight median 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.''
 <br>
-[[File:U-turn_Parallel_Check_Curved.png]]
+[[File:U-turn_Parallel_Check_Curved.png||680px]]
 <br>
-==== {{@|Common mistakes}} ====
+==== {{@|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>

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