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

Revision as of 12:58, 25 August 2015

Median U-turn penalty

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

The Waze routing algorithm assesses a penalty for a double-left or double-right turn, which can be used to prevent U-turns at H-style intersections on divided and parallel roads.

Preventing median U-turns

A large U-turn penalty is applied 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:
an incoming segment, a single median segment, and an outgoing segment
The length of the median segment is shorter than 15 m (49.21 feet)
The incoming and outgoing segments 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 a median segment, break any one of the above criteria. For example:

To allow median U-turns in both directions, break condition #2 by making the median segment longer than 15 m (49.21 ft)
To selectively allow a U-turn from only one direction, first setup U-turn prevention as you would for both directions. For the side where U-turns are allowed, make the incoming and outgoing segments sufficiently non-parallel. (Tip: consider using a Micro-dogleg to discreetly tweak the angle without affecting appearance)

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. These two segments are considered parallel if their angles with respect to a straight median segment sum to 180±5º (i.e, between 175º and 185º).

Angles can be easily checked with the Junction Angle Info script add-on, which can be set to report absolute angles or turn angles ("departure"). For the purpose of determining parallelism, summing either measurements will work.

However, if the median segment has geometry nodes and is not straight, it cannot be used as a reference. In this case, temporarily add a straight segment to the same junctions as the existing curved median. Check the angles using this straight median and delete when done.

@@ 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].}}
-{{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.
+[[File:U-turn_Roads.png||360px|right]]
+The Waze routing algorithm assesses a [[Routing penalties#Road_configurations|penalty]] for a double-left or double-right turn, which can be used to prevent U-turns at H-style intersections on divided and parallel roads.
 ==== {{@|Preventing median U-turns}} ====
+A large U-turn penalty is applied for a double-left or double-right turn when '''''all three''''' of the conditions below are met:
-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 U-turn involves a reversal of driving direction through 3 segments: <br>an incoming segment, a single median segment, and an outgoing segment
+# The length of the median segment is shorter than 15 m (49.21 feet)
+# The incoming and outgoing segments 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]}}
+<br>
-# The forbidden U-turn is composed of one incoming segment, one median segment, and one outgoing segment.
+==== {{@|Allowing median U-turns}} ====
-# 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 double-left or double-right turn through a median segment, break any one of the [[#Preventing median U-turns|above criteria]]. For example:
-To allow a U-turn through a median, ensure that any one of the [[#Preventing median U-turns|above criteria]] are broken:
+* To allow median U-turns in both directions, break condition #2 by making the median segment longer than 15 m (49.21 ft)
+* To selectively allow a U-turn from only one direction, first setup U-turn prevention as you would for both directions. For the side where U-turns are allowed, make the incoming and outgoing segments sufficiently [[#Checking for parallel segments|non-parallel]]. (Tip: consider using a [[Glossary#mDL|Micro-dogleg]] to discreetly tweak the angle without affecting appearance)
+<br>
-* To allow the median U-turn in both directions, it is simplest to make the median segment longer than 15 meters. ''(Breaking condition #2)''
+==== {{@|Checking for parallel incoming and outgoing segments}} ====
-* 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}} ====
+Condition #3 for U-turn prevention requires the incoming and outgoing segments to be within ±5º of parallel to each other. These two segments are considered parallel if their angles with respect to a ''straight'' median segment sum to 180±5º (i.e, between 175º and 185º).
-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.''
+Angles can be easily checked with the [[Scripts#WME_Junction_Angle_info|Junction Angle Info]] script add-on, which can be set to report absolute angles or [[How_Waze_determines_turn_/_keep_/_exit_maneuvers|turn angles]] ("departure"). For the purpose of determining parallelism, summing either measurements will work.
+<br>
+[[File:U-turn_Parallel_Check_Straight.png||center]]
-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.
+However, if the median segment has geometry nodes and is not straight, it cannot be used as a reference. In this case, temporarily add a straight segment to the same junctions as the existing curved median. Check the angles using this straight median and delete when done.
+<br>
+[[File:U-turn_Parallel_Check_Curved.png]]
+<br>
-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.
+==== {{@|Common mistakes}} ====
-[[File:LilyPondU-turn.jpeg]]