Cannot U-turn at Boul de l'Acadie / Rue de Louvain Ouest

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Cannot U-turn at Boul de l'Acadie / Rue de Louvain Ouest

Postby vincentSunny » Fri Feb 05, 2016 6:58 pm

Can anyone verify why I cannot make U-turn at Boul de l'Acadie? I checked the map editor and U-turn is allowed.

Directions:
http://imgur.com/tbOkYGh

Link to the editor:
https://www.waze.com/editor/?env=usa&lo ... 997&zoom=7
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Re: Cannot U-turn at Boul de l'Acadie / Rue de Louvain Ouest

Postby phil-mtl » Fri Feb 05, 2016 7:32 pm

You're right, the U-turn should be allowed. There's even a sign that specifically says so, which is not something I'm used to seeing in Montreal.

Why won't Waze route you through it, even though all turns are allowed? Well, the rules for U-turn in box intersections are somewhat arcane. Basically, even if you allow all turns, Waze won't route you through this U-turn if three conditions 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).
As a safety margin, leave a 1 m buffer zone by using 14 meters (45.93 feet) or less.

In/out parallelism: The in and out segments (A and C) are within ±5° of parallel to each other.


You can read more on the subject in the wiki.

I went ahead and broke one of the three conditions, by lengthening the median segment. Here's the before:
[ img ]

and here's the after:
[ img ]

Waze should, after the next tile update, route you through the U-turn.
Last edited by phil-mtl on Fri Feb 05, 2016 7:39 pm, edited 1 time in total.
[ img ]
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Re: Cannot U-turn at Boul de l'Acadie / Rue de Louvain Ouest

Postby vincentSunny » Fri Feb 05, 2016 7:38 pm

Thanks a lot!
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Re: Cannot U-turn at Boul de l'Acadie / Rue de Louvain Ouest

Postby hmarian » Fri Feb 05, 2016 7:43 pm

Phil is correct.
Waze tend to avoid u-turn on segments shorter than 15m.
But please keep in mind that this rule is not absolute and since it is prevented based on penalty added to the turn we have seen cases that Waze allowed u-turns on segments shorter than 15m.

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