Routing penalties/Controlling U-turn penalties
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The Waze routing algorithm has a method of penalizing some double-left and double-right turns. This can prevent U-turns at H or # style intersections on divided and parallel roads.
It is 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 is illegal or impossible, disallow that turn instead. The U-turn will then not be routed, and the following penalty does not matter.
Contents
Preventing median U-turns
An extremely 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 equal to 45.93 ft (14 m) or less.
- 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 it immediately follows a reroute. If you observe this method to fail in other situations when it is implemented properly, please report it in this forum thread |
Allowing median U-turns
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To allow median U-turns in both directions, break condition #2 by making the median segment (B) 52.49 ft (16 m) or longer
To allow a U-turn from only one direction, first setup the intersection to allow U-turns in both directions. Then, add a Junction Box, and restrict the prohibited U-turn route. As of 2017^{[update]}, a rank 5 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^{[update]}, Waze staff has expressed a preference that map editors use Junction Boxes in these situations. |
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 is straight, sum the two angles making up the U-turn:
- The angle between the incoming and median segments (between A and B)
- 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
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. |
Additional examples
Example | Tip | Details |
---|---|---|
Cutting a median segment into two may have unintended consequences | U-turns are legal at this intersection. Even though U-turn prevention will not be 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 can trigger a lower penalty mechanism designed to discourage detours off the main road (see 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. Furthermore, BDP might not trigger here if all of its criteria are not met. | |
A median segment 52.49 ft (16 m) or longer 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 the divided road is small. Ensure the U-turn segment is 52.49 ft (16 m) or longer by adjusting geometry. A median segment of any shape can trigger a U-turn penalty between parallel roads if it is not long enough. | |
To ensure proper routing between two closely spaced parallel roads, connect the two with a segment 52.49 ft (16 m) or longer | 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 for one way or two way segments. |