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

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

− | To allow a | + | To allow a double left/right turn through a median segment, break any one of the [[#Preventing median U-turns|above criteria]]. |

+ | <br>For example: | ||

− | * To allow | + | * To allow median U-turns in both directions, break condition #2 by making the median segment longer than 15 m (49.21 ft) |

− | * To allow | + | * To selectively allow a U-turn from only one direction, first setup U-turn prevention as you would for both directions. Then, 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 adjust the angle without affecting appearance) |

==== {{@|Checking for parallel segments}} ==== | ==== {{@|Checking for parallel segments}} ==== |

## Revision as of 04:48, 24 August 2015

## Contents

### Median U-turn penalty

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

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 |

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

#### Preventing median U-turns

A large U-turn penalty is applied for a double left/right turn when * all three* of the conditions below are met:

- The U-turn is composed of 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

#### Allowing median U-turns

To allow a double left/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. Then, 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 adjust the angle without affecting appearance)

#### Checking for parallel segments

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.*

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.

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.