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

## 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 whether to apply a penalty for a double-left or -right turn. This can be used to prevent U-turns at box- (#) and H-style intersections on divided highways and parallel roads.

#### Preventing median U-turns

U-turns via a median segment are heavily 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.

1. The forbidden U-turn is composed of one incoming segment, one median segment, and one outgoing segment.
2. The length of the median segment is shorter than 15 m (49 feet).
3. The portion of those two segments closest to the median segment must be within ±5° of exactly parallel.

#### Allowing median U-turns

To allow a U-turn through a median, ensure that any one of the above criteria are broken:

• To allow the median U-turn in both directions, it is simplest to make the median segment longer than 15 meters. (Breaking condition #2)
• 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 ±5° allowance of exactly parallel. This is easily achieved without affecting the overall look of the map using a Micro-dogleg.

#### 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:

1. X — the angle between the incoming one-way segment and the reference segment
2. 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.