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

(→{{@|Checking for parallel incoming and outgoing segments}}: slightly simpler words. Segment A, B, and C) |
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{{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|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]] | [[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. | 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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A large U-turn penalty is set for a double-left or double-right turn when '''''all three''''' of the conditions below are met: | 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 | + | # '''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). |

− | # | + | # '''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 [[#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> | <br> | ||

==== {{@|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 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 | + | * 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. | + | * 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> | <br> | ||

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

− | Condition #3 for U-turn prevention requires the | + | 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 [[How_Waze_determines_turn_/_keep_/_exit_maneuvers|turn angles]]; using either is OK. |

− | If segment B is straight, | + | ===== {{@|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 {{font color|red|between 175º and 185º}}, the in and out segments (A and C) are considered parallel. | ||

<br> | <br> | ||

− | [[File:U-turn_Parallel_Check_Straight.png|| | + | [[File:U-turn_Parallel_Check_Straight.png||680px]] |

+ | |||

+ | ===== {{@|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.'' | |

<br> | <br> | ||

− | [[File:U-turn_Parallel_Check_Curved.png]] | + | [[File:U-turn_Parallel_Check_Curved.png||680px]] |

<br> | <br> | ||

− | ==== {{@| | + | ==== {{@|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> |

## Revision as of 05:19, 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:

**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. |