Junction Style Guide/Intersections: Difference between revisions Discussion View history

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{{ReturnTo | Junction_Style_Guide | the Junction Style Guide}}


== Three-way ==
== Three-way ==
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{| class="Wikitable floatleft"
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| [[Image:Jct_3_45_ex.png|border]]
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Here is a completed real world example which provides the expected turn instructions and "catches" turns from all directions avoiding automatic problems for [[Map_Problems_in_Waze_Map_Editor#Missing_road|missing road]] when they are "too far apart."
Here is a completed real world example which provides the expected turn instructions and "catches" turns from all directions avoiding automatic problems for [[Map_Problems_in_Waze_Map_Editor#Missing_road|missing road]] when they are "too far apart."
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For conditions where the straight through route changes road names, it is important to identify which segment is drawn as the straight route and which is shown as the right turn from the main road. As the [[How_Waze_determines_turn_/_keep_/_exit_maneuvers|How Waze Determines turn/keep/exit maneuvers]] page explains, segment names and geometry are very important in determining what navigation instructions are given.
For conditions where the straight through route changes road names, it is important to identify which segment is drawn as the straight route and which is shown as the right turn from the main road. As the [[How_Waze_determines_turn_/_keep_/_exit_maneuvers|How Waze Determines turn/keep/exit maneuvers]] page explains, segment names and geometry are very important in determining what navigation instructions are given.


[[Image:Jct_Y_ex_aerial.png|right|border]]
[[Image:Jct_Y_ex_aerial.png|200px|right|border]]
In this example to the right, the multi-lane surface street is known as Main Street to the west and Atlantic Ave. to the east. The name change occurs when Main St. branches off as a regular surface street. That is the human description, but a more technical description would be that Main St. travels in a perfectly straight line and Atlantic Ave. branches off of it. But if we map it that way in the editor, we create a major problem.
In this example to the right, the multi-lane surface street is known as Main Street to the west and Atlantic Ave. to the east. The name change occurs when Main St. branches off as a regular surface street. That is the human description, but a more technical description would be that Main St. travels in a perfectly straight line and Atlantic Ave. branches off of it. But if we map it that way in the editor, we create a major problem.
{{clear}}
{{clear}}


[[Image:Jct_Y_ex_map_bad.png|left|border]]
[[Image:Jct_Y_ex_map_bad.png|200px|left|border]]
Since the multi-lane segment of Main St. and the regular street segment of Main St. have the same name, the routing engine automatically considers that to be "straight". If the two sections line up in a straight line the way they appear from the sky, then we are reinforcing the idea that "straight" is Main St. to Main St. But as a typical driver would want, "straight" should be the path that remains on the multi-lane roadway, regardless of what name it uses.
Since the multi-lane segment of Main St. and the regular street segment of Main St. have the same name, the routing engine automatically considers that to be "straight". If the two sections line up in a straight line the way they appear from the sky, then we are reinforcing the idea that "straight" is Main St. to Main St. But as a typical driver would want, "straight" should be the path that remains on the multi-lane roadway, regardless of what name it uses.
{{clear}}
{{clear}}


[[Image:Jct_Y_ex_map.png|right|border]]
[[Image:Jct_Y_ex_map.png|200px|right|border]]
To make sure the routing engine understands the proper treatment of the junction, we have to be deliberate with the segment geometry of all three involved segments.  We end up with something like the image on the right. Now the geometric definition of straight is the multi-lane portion of Main St. onto Atlantic Ave., since we have made that transition as close to zero degrees as possible. The regular street portion of Main St. now branches off at an angle close to 90 degrees. The routing engine should recognize that a turn is required. So the result is that Main St. to Atlantic Ave. has no announced turn, and multi-lane Main St. to surface road Main St. has a turn announced. Exactly what most drivers would expect in the real world.
To make sure the routing engine understands the proper treatment of the junction, we have to be deliberate with the segment geometry of all three involved segments.  We end up with something like the image on the right. Now the geometric definition of straight is the multi-lane portion of Main St. onto Atlantic Ave., since we have made that transition as close to zero degrees as possible. The regular street portion of Main St. now branches off at an angle close to 90 degrees. The routing engine should recognize that a turn is required. So the result is that Main St. to Atlantic Ave. has no announced turn, and multi-lane Main St. to surface road Main St. has a turn announced. Exactly what most drivers would expect in the real world.


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Therefore add one more geometry node to make the departure angle at the junction closer to 10 or 20 degrees. (dogleg) See the discussion on [[Junction Style Guide#Controlling Turn Instructions|controlling turn instructions]] for details on those angles. Now the arrows are visible and accessible. Note that also pressing '''s''' in the editor will '''s'''pread or '''s'''eparate the arrows at a junction, if a arrow is still difficult to reach. See the [[Keyboard shortcut|keyboard shortcuts]] article for more tips on other keys.
Therefore, add one more geometry node to make the departure angle at the junction closer to 10 or 20 degrees. (dogleg) See the discussion on [[Junction Style Guide#Controlling Turn Instructions|controlling turn instructions]] for details on those angles. Now the arrows are visible and accessible. Note that also pressing '''s''' in the editor will '''s'''pread or '''s'''eparate the arrows at a junction, if an arrow is still difficult to reach. See the [[Keyboard shortcut|keyboard shortcuts]] article for more tips on other keys.


With this adjusted angle, this junction now behaves as expected and the turn restrictions can be easily accessed. {{clear}}
With this adjusted angle, this junction now behaves as expected and the turn restrictions can be easily accessed. {{clear}}
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{{clear}}
{{clear}}


== Split road intersections ==
== {{anchor|Split road intersections}}Divided road intersections==
Many of the principles stated above apply to intersections between split roads. Usually, split road intersections should represent reality.
Many of the principles stated above apply to intersections between divided roads. Usually, divided road intersections should look like the traffic lanes they represent. "Box" shaped intersections are easiest to draw, maintain, and to explain to other editors.  Only use variations when they are needed.


{{NeedInfo|Insert examples of a split road intersecting an unsplit road, two split roads intersecting each other, 3-way intersections involving split roads, intersections where one road changes between split/unsplit at the intersection...}}
Read through the pros and cons of the intersection types below and select the best suited.


When the name of a road is different on either side of a split road intersection, leave the median segment unnamed. This way, Waze will use the correct name when instructing the user to make a left turn.
{{NeedInfo|Insert examples of a divided road intersecting a two-way road, two divided roads intersecting each other, 3-way intersections involving divided roads, intersections where one road changes between  divided/2-way at the intersection...}}


=== Three way ===
=== Box and partial box intersections ===


Three way split road intersections are easier to edit accurately than four way intersections.
This type of intersection is most useful in intersections where the traffic queues in a median segment that is long enough to justify being mapped, especially if the one-way roads would have to deviate greatly from their physical location to meet in a single point for a bow tie. This also allows the map to route correctly while representing the actual geometry of the roads in real life, which is more intuitive to users.


{{NeedInfo|Insert examples: split road ends at unsplit road (single point if both lefts are allowed and u turns are not); split road ends at split road ("triangle" in median if both lefts are allowed and u turns are not); unsplit road ends at split road (easy).}}
Do not use this type of junction if the crossbar will be less than {{:Segment length/Minimum}}. Waze has difficulty in capturing average speeds for short segments, especially in wide intersections where traffic travels a fairly curved path rather than sticking close to the segment.  Add in the inaccuracy of many phone GPS units, and you may have a situation where the reported positions of some of the vehicles are never on the segment during the maneuver.


[[Image:3wayunsplitsplit.png]]
When creating three way and four way intersections, if the cross street changes names at the junction, make sure that the segment(s) have no name. This will cause the segment to inherit the appropriate name depending on the direction of travel.  This center segment will not be included when you choose "Select entire street".


Three way divided road intersections are easier to edit accurately than four way intersections.


{{NeedInfo|Insert examples: divided road ends at 2-way road (single point if both lefts are allowed and u turns are not); divided road ends at divided road ("triangle" in median if both lefts are allowed and u turns are not); 2-way road ends at divided road (easy).}}


=== Four way ===
[[Image:3wayunsplitsplit.png]]
 
Four way split road intersections can often be constructed in Waze to represent reality – however, in some circumstances, alternative methods must be used.


When all split-road U turns are allowed at an intersection, or when disallowed U turns are effectively restricted in Waze by existing restricted left turns already, use the guidance in this immediate section.
If possible, lay out the intersection to resemble reality.  When all divided-road U turns are allowed at an intersection, or when disallowed U turns are effectively restricted in Waze by existing restricted left turns already, use the guidance in this section.


When a U turn must be restricted, but both of the left turns that make up that U turn are allowed on their own, follow the guidance in [[#Avoiding U turns|Avoiding U turns]] below.
When a U turn must be restricted, but both of the left turns that make up that U turn are allowed on their own, follow the guidance in [[#Avoiding U turns|Avoiding U turns]] below.


{{NeedInfo|Insert examples: split road intersects an unsplit road (≠); two split roads intersect (#); intersection where one road changes between split/unsplit at the intersection...}}
{{NeedInfo|Insert examples: divided road intersects a 2-way road (≠); two divided roads intersect (#); intersection where one road changes between divided/2-way at the intersection...}}


{| class="wikitable"
{| class="wikitable"
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! Intersection style !! Example
! Intersection style !! Example
|-
|-
| A split road intersecting a split road. || [[Image:4waysplitsplit.png|300px]]
| A divided road intersecting a divided road. || [[Image:4waysplitsplit.png|300px]]
|-
|-
| A split road intersecting an unsplit road. || [[Image:4waysplitunsplit.png|300px]]
| A divided road intersecting a 2-way road. || [[Image:4waysplitunsplit.png|300px]]
|-
|-
| A transitioning (split-unsplit) road intersecting an unsplit road. || [[Image:Split_road_to_sinlge_road.png|300px]]
| A transitioning (divided-2-way) road intersecting a 2-way road. || [[Image:Split_road_to_sinlge_road.png|300px]]
|-
|-
| A transitioning (split-unsplit) road intersecting a split road. || (image)
| A transitioning (divided-2-way) road intersecting a divided road. || (image)
|-
|-
| Be careful with your geometry – following the center of the actual road too closely can lead to rather high turn angles, and therefore possibly unwanted turn instructions. Keep it smooth. || [[Image:Transition.png|300px]]
| Be careful with your geometry – following the center of the actual road too closely can lead to rather high turn angles, and therefore possibly unwanted turn instructions. Keep it smooth. || [[Image:Transition.png|300px]]
|}
|}


=== Bow tie ===
{{Anchor|Bowtie}}


=== Avoiding U turns ===
[[File:Jct_bowtie.png|301px|thumbnail|right|The bow tie intersection is NOT RECOMMENDED]]The bow tie intersection is no longer the best way to take control of turns and traffic at divided-road intersections. It is an unrealistic representation of an intersection and drivers report map errors based on this appearance. It was necessary before the introduction of the [[junction box]] and the 3-segment U-turn prevention mechanism, but now there are better methods to control turns and properly account for queuing.
 
 
At a particular split road intersection, in a case where a U turn is not allowed, but both of the left turns that make up that U turn are allowed separately, one of the following alternate intersection methods may be used.
 
 
These are only necessary when at least one road is split on both sides of the intersection. (Where two split roads, or a split road and an unsplit road meet).
 
Alternative methods to standard turn restrictions are not necessary at 3-way intersections involving split roads.


* Where Waze seems to be doing a poor job of keeping track of traffic queuing, a junction box is recommended.
* To prevent U-turns, rely on the u-turn prevention mechanism below.
* In complicated situations, control u-turns using a junction box.
* Do not add new bow ties to the map.
* When you find a bow tie intersection on the map, check if it can be replaced by a realistically drawn intersection using other techniques to control turns and traffic.
* If you think it is necessary to add a bow tie to the map, contact state managers to discuss the intersection. They will most likely recommend a better approach.


Use a [[#Bow tie|bow tie]] where the separation between the parallel roads is less than {{:Segment length/Minimum}}, you may want to also consider un-splitting the road.
=== Avoiding U-turns in box and partial box intersections ===
{{anchor|Avoiding U turns|Avoiding U turns in box and partial box intersections}}
{{:Routing penalties/Controlling U-turn penalties}}


==== H junction or box junction====
[[File:MinSegLengthUturn2.png|border|390px|right|Segment too short to allow two left turns]]
U-turns can be avoided where two split roads intersect (in a # configuration, aka a Box junction) or a split road intersects an unsplit road (in an H configuration junction)
* The length of the median segment (the "H" cross-bar) is less than {{:Routing penalties/U-turn minimum}}.
* The two parallel segments of the split road being used for the U-turn are one-way segments.
* The two parallel segments of the split road being used for the U-turn are approximately parallel to each other.
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.
{{Mbox|type=speculation|text=It is currently assumed that the method used to determine if roads are parallel is by looking at the turn angles. If the sum of the two turn angles which make up the U-turn equals approximately 180°, the roads will be considered parallel. There may be little leeway here, so try to get as close to 180° as possible.}}
This type of intersection is most useful in intersections where the traffic queues in the space within the medians and is long enough to justify being mapped, especially if the one-way roads would have to deviate greatly from their physical location to meet in a single point for a bow tie. This also allows the map to route correctly while representing the actual geometry of the roads in real life, which is more intuitive to users.
Do not use an H junction if the crossbar will be less than {{:Segment length/Minimum}}. Waze has difficulty in capturing average speeds for short segments, especially in wide intersections where traffic travels a fairly curved path rather than sticking close to the segment.  Add in the inaccuracy of many phone GPS units, and you may have a situation where the reported positions of some of the vehicles are never on the segment during the maneuver.
If the cross street changes names at the junction, make sure that the segment(s) have no name. This will cause the segment to inherit the appropriate name depending on the direction of travel.  This center segment will not be included when you choose "Select entire street".
  {{clear}}
  {{clear}}
 
{{ReturnTo | Junction_Style_Guide | the Junction Style Guide}}
==== Bow tie ====
[[Category:Style Guide]]
{{Anchor|Bowtie}}
 
[[File:Jct_bowtie.png|right]]
Gaining control of turns by reducing the intersection to a single point.
 
The "bow tie" intersection method also allows the restriction of U turns without restricting the left turns that make up the U turn.
Use it only
* at 4-way split road intersections (between two split roads, or between a split road and an unsplit road).
* only when necessary to prevent u-turns while allowing left-hand turns.
* The angles at the single bow tie intersection can reasonably be made 45 degrees or less. Otherwise, drivers going straight through will get an instruction to turn or stay right in [[right-hand traffic]] countries (turn or stay left in [[left-hand traffic]] countries)
 
 
{{ReturnJSG}}

Revision as of 05:45, 8 May 2018

This revision of a section is currently undergoing modifications. The information presented should be considered a draft, not yet ready for use. Content is being prepared by one or more users. Do not make any changes before you send a private message to this user. Please use the talk page for thoughts and ideas on setting up this content.

Three-way

Right angles

The simplest junctions often resemble a "T" and are considered diverging or branch roads. The branch road will normally meet the main road at nearly a 90 degree angle. This is the simplest situation to map, as the physical and logical views of the roads match up well.

Odd angles

Some roads meet at odd angles. The initial urge will be to represent the junction as it is in the physical world - two lines running into each other at a sharp angle. But there are issues with this method.

  • Depending on the angle, the client may give a "Keep Right" instruction to the driver when a "Turn Right" instruction is more appropriate. If Minor Highways or above are involved, you will actually get an "Exit Right" which can be confusing in many situations.
  • In some cases, no instruction will be given at all. In the worst case, the routing server may determine that it isn't possible to make a very sharp turn angle and not suggest the turn at all (in the example image, heading south, then turning left, to head east).
  • Automatic map errors may appear with turns from one direction as the path of the turning traffic is "too far" away from the actual junction (in this example, traveling south, then turning left to head east).

To eliminate ambiguity, map the junction from a logical point of view. Since basic "Turn Left" and "Turn Right" instructions are desired, tweak the intersecting angle so it resembles a basic 90 degree intersection. Add geometry nodes to make the branch road leave the main road at close to 90 degrees, then gradually curve the road to match the true departure angle. This will produce a junction that logically works like a basic 90 degree junction, but it also fits the reality of the physical world.

Here is a completed real world example which provides the expected turn instructions and "catches" turns from all directions avoiding automatic problems for missing road when they are "too far apart."

Name changes on straight path

For conditions where the straight through route changes road names, it is important to identify which segment is drawn as the straight route and which is shown as the right turn from the main road. As the How Waze Determines turn/keep/exit maneuvers page explains, segment names and geometry are very important in determining what navigation instructions are given.

In this example to the right, the multi-lane surface street is known as Main Street to the west and Atlantic Ave. to the east. The name change occurs when Main St. branches off as a regular surface street. That is the human description, but a more technical description would be that Main St. travels in a perfectly straight line and Atlantic Ave. branches off of it. But if we map it that way in the editor, we create a major problem.

Since the multi-lane segment of Main St. and the regular street segment of Main St. have the same name, the routing engine automatically considers that to be "straight". If the two sections line up in a straight line the way they appear from the sky, then we are reinforcing the idea that "straight" is Main St. to Main St. But as a typical driver would want, "straight" should be the path that remains on the multi-lane roadway, regardless of what name it uses.

To make sure the routing engine understands the proper treatment of the junction, we have to be deliberate with the segment geometry of all three involved segments. We end up with something like the image on the right. Now the geometric definition of straight is the multi-lane portion of Main St. onto Atlantic Ave., since we have made that transition as close to zero degrees as possible. The regular street portion of Main St. now branches off at an angle close to 90 degrees. The routing engine should recognize that a turn is required. So the result is that Main St. to Atlantic Ave. has no announced turn, and multi-lane Main St. to surface road Main St. has a turn announced. Exactly what most drivers would expect in the real world.

Steep angles with exits and keep right or left

Jct ramp no geo.png Jct ramp no geo arrow.png

A ramp from a highway is another good example where additional geometry nodes are helpful. Especially since most ramps diverge at a very small angle from the road. The drawback in this case is it may be hard to see and click on the turn restriction arrows in the editor.

Jct ramp w geo.png Jct ramp w geo arrow.png

Therefore, add one more geometry node to make the departure angle at the junction closer to 10 or 20 degrees. (dogleg) See the discussion on controlling turn instructions for details on those angles. Now the arrows are visible and accessible. Note that also pressing s in the editor will spread or separate the arrows at a junction, if an arrow is still difficult to reach. See the keyboard shortcuts article for more tips on other keys.

With this adjusted angle, this junction now behaves as expected and the turn restrictions can be easily accessed.

Four-way

Right angles

The second simplest junction category is a "+" or "cross" four-way junction that intersects at 90 degrees. These roads are simple to map as the logical and physical views of the roads match up well. These instructions follow the similar guidelines and solve the same problems as diverging roads.

Odd angles

Similar to diverging roads that intersect at odd angles, crossing roads can do the same thing. When these intersections are mapped as seen here with these odd angles, complications can occur.

Geometry nodes bring the actual junction close to 90 degrees. Zoom in to the intersection and add a single geometry node on each side as close to the junction point as possible. This will give the more desirable 90 degree angle, and it will still be virtually invisible to client app users making it look like the physical world. This image is what is seen when zoomed in as close as possible. Zoomed back out, it looks just like the map image showing the junction without any geometry nodes.

Here is a real world example at a close zoom level where you can still see the geometry adjustment. With that adjustment in place, the junction will produce predictable turn left and right navigation instructions while the roads still appear to meet at the real-world angle in the client app.

Divided road intersections

Many of the principles stated above apply to intersections between divided roads. Usually, divided road intersections should look like the traffic lanes they represent. "Box" shaped intersections are easiest to draw, maintain, and to explain to other editors. Only use variations when they are needed.

Read through the pros and cons of the intersection types below and select the best suited.

Insert examples of a divided road intersecting a two-way road, two divided roads intersecting each other, 3-way intersections involving divided roads, intersections where one road changes between divided/2-way at the intersection...

Box and partial box intersections

This type of intersection is most useful in intersections where the traffic queues in a median segment that is long enough to justify being mapped, especially if the one-way roads would have to deviate greatly from their physical location to meet in a single point for a bow tie. This also allows the map to route correctly while representing the actual geometry of the roads in real life, which is more intuitive to users.

Do not use this type of junction if the crossbar will be less than 19.69 ft (6 m). Waze has difficulty in capturing average speeds for short segments, especially in wide intersections where traffic travels a fairly curved path rather than sticking close to the segment. Add in the inaccuracy of many phone GPS units, and you may have a situation where the reported positions of some of the vehicles are never on the segment during the maneuver.

When creating three way and four way intersections, if the cross street changes names at the junction, make sure that the segment(s) have no name. This will cause the segment to inherit the appropriate name depending on the direction of travel. This center segment will not be included when you choose "Select entire street".

Three way divided road intersections are easier to edit accurately than four way intersections.

Insert examples: divided road ends at 2-way road (single point if both lefts are allowed and u turns are not); divided road ends at divided road ("triangle" in median if both lefts are allowed and u turns are not); 2-way road ends at divided road (easy).

If possible, lay out the intersection to resemble reality. When all divided-road U turns are allowed at an intersection, or when disallowed U turns are effectively restricted in Waze by existing restricted left turns already, use the guidance in this section.

When a U turn must be restricted, but both of the left turns that make up that U turn are allowed on their own, follow the guidance in Avoiding U turns below.

Insert examples: divided road intersects a 2-way road (≠); two divided roads intersect (#); intersection where one road changes between divided/2-way at the intersection...
Intersection style Example
A divided road intersecting a divided road.
A divided road intersecting a 2-way road.
A transitioning (divided-2-way) road intersecting a 2-way road.
A transitioning (divided-2-way) road intersecting a divided road. (image)
Be careful with your geometry – following the center of the actual road too closely can lead to rather high turn angles, and therefore possibly unwanted turn instructions. Keep it smooth.

Bow tie

The bow tie intersection is NOT RECOMMENDED

The bow tie intersection is no longer the best way to take control of turns and traffic at divided-road intersections. It is an unrealistic representation of an intersection and drivers report map errors based on this appearance. It was necessary before the introduction of the junction box and the 3-segment U-turn prevention mechanism, but now there are better methods to control turns and properly account for queuing.

  • Where Waze seems to be doing a poor job of keeping track of traffic queuing, a junction box is recommended.
  • To prevent U-turns, rely on the u-turn prevention mechanism below.
  • In complicated situations, control u-turns using a junction box.
  • Do not add new bow ties to the map.
  • When you find a bow tie intersection on the map, check if it can be replaced by a realistically drawn intersection using other techniques to control turns and traffic.
  • If you think it is necessary to add a bow tie to the map, contact state managers to discuss the intersection. They will most likely recommend a better approach.

Avoiding U-turns in box and partial box intersections


As of December 2021, the Waze routing algorithm penalizing some double-left and double-right turns has been disabled in the United States. The routing server will no longer automatically avoid double-left turns. To prevent u-turns on divided roads, use a Junction box.


Note: The road types displayed in the images might not match the standards for where you edit. Please check your local wiki and with local experts to learn the correct road type to use for median segments in your area.

Historic U-turn routing prevention

The Waze routing algorithm previously had a method of penalizing some double-left and double-right turns. This used to prevent U-turns at H or # style intersections on divided and parallel roads. Expand the section below to learn how this used to work.

It was useful for preventing the sequence of two turns that would make up the U-turn, while still allowing the individual turns. However, if either of the two turns making up the U-turn was illegal or impossible, it would disallow that turn instead. The U-turn would then not be routed, and the following penalty would not matter.


Preventing median U-turns link to this section

An extremely large U-turn penalty was set for a double-left or double-right turn when all three of the conditions below were met:

  1. 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).
  2. Short median: The median segment (B) is equal to 45.93 ft (14 m) or less.
  3. In/out parallelism: The in and out segments (A and C) are within ±5° of parallel to each other.


It was possible for this method to fail to prevent a U-turn when it was the first segment of a route, or it immediately followed a reroute. Previously, if you observed this method to fail in other situations when it is implemented properly, you would report it in this forum thread.


Previously, to allow median U-turns in both directions, you would break condition #2 by making the median segment (B) 52.49 ft (16 m) or longer.

Previously, to allow a U-turn from only one direction, you would first setup the intersection to allow U-turns in both directions. Then, add a Junction Box, and restrict the prohibited U-turn route. A rank 4 user or above is required to install a Junction Box.

Previously, unidirectional U-turn prohibition on a divided road was set up by breaking condition #3 of the U-turn prevention mechanism through the use of a micro-dogleg. As of 2017, Waze staff has expressed a preference that map editors use Junction Boxes in these situations.


Checking for parallel incoming and outgoing segments link to this section

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 link to this section

If the median segment is straight, sum the two angles making up the U-turn:

  1. The angle between the incoming and median segments (between A and B)
  2. The angle between the median and outgoing segments (between B and C)

The in and out segments (A and C) are considered parallel if the sum is between 175º and 185º.

The short 14m median segment in the above examples satisfies condition #2 for U-turn prevention.
Curved median segments link to this section

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.

Be sure the 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.

Click Expand for details on workaround options when any segments connected to either junction node cannot be edited.

  1. Disable the WME setting "Draw new roads with all turns allowed" before drawing the new segment.
  2. Draw the new segment disconnected from any other segment, then drag the end nodes to connect to the junctions.

Please see the Controlling U-turn penalties article for more advanced details, and additional examples.