# Difference between revisions of "Routing penalties/Controlling U-turn penalties"

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− | === {{@| | + | === {{@|Median U-turn penalty}} === |

{{anchor|Avoiding U turns|Avoiding U turns in box and partial box intersections}} | {{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=forum | + | |

[[File:U-turn_Roads.png||360px|right]] | [[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 | + | 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. |

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==== {{@|Preventing median U-turns}} ==== | ==== {{@|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: | |

− | # | + | # 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 |

− | # | + | # Segment B is shorter than 15 m (49.21 feet) |

− | # | + | # Segment A and segment B 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]}} | ||

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==== {{@|Allowing median U-turns}} ==== | ==== {{@|Allowing median U-turns}} ==== | ||

− | To allow a double-left or double-right turn through | + | 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 median U-turns in both directions, break condition #2 by making the median segment | + | * 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 a U-turn from only one direction, first set up U-turn prevention for both directions. | + | * 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. |

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==== {{@|Checking for parallel incoming and outgoing segments}} ==== | ==== {{@|Checking for parallel incoming and outgoing segments}} ==== | ||

− | Condition #3 for U-turn prevention requires | + | 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. |

− | + | 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. | |

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− | + | [[File:U-turn_Parallel_Check_Straight.png||center]] | |

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− | + | 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 | |

− | If | ||

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− | [[File:U-turn_Parallel_Check_Curved.png | + | [[File:U-turn_Parallel_Check_Curved.png]] |

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− | ==== {{@| | + | ==== {{@|Common mistakes}} ==== |

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## Revision as of 17:10, 30 September 2015

### 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:

- The U-turn involves a reversal of driving direction through 3 segments:

A) an incoming segment, B) a single median segment, and C) an outgoing segment - Segment B is shorter than 15 m (49.21 feet)
- Segment A and segment B 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 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 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 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 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 Junction Angle Info (JAI) browser extension to measure the angles. JAI may be set for absolute or turn angles; either setting 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.

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