It looks to me like the U-turn is prevented as it looks like it meets all the criteria discussed here. I think making this segment longer than 15 m would permit the U-turn.

I'm curious as to the destination. Was the ultimate destination close to the U-turn, was the U-turn part of a U/right to avoid a left turn, or something else?

I'll be interested to hear what staff says. Seems to me the question is: why is the U-turn at 60th prevented but not the U-turn at 58th?

Hmm, I had no problem at all getting the live map to route the U at 58A, like in Kayos's screenshot.

https://www.waze.com/livemap?lon=-122.7 ... t_text=Now

I would also assume that the BDP effects around the block U turns here.

Another example of u-turn route allowed when it appears the rules are being followed correctly to prevent it. Median has no geometry and is 13.8 m, total angle of incoming / outgoing segments is 183 deg.

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Cheers

PesachZ wrote:The roads were edited today to make the median smaller, but that wasnt necessary. If you test it in livemap you'll see you can't reproduce that route. From the UR trace it does seem like it was a recalcuation on that last segment before the uturn, which is a known cause of prevention failure.

With enough persistence I am able to reproduce a u-turn at that intersection in livemap:



I had to try several variations on a theme, but eventually I was given the u-turn as a suggested route. The editor who responded to the UR has indicated that this intersection has historically suggested sporadic and infrequent u-turns.

I notice that the route saved by the UR u-turned on Boul Laurier then headed south on Aut 73. The wazer instead headed north on Aut 73. Was this what made you think a recalculation was involved? I'm not sure I follow.

At any rate, I do seem to be able to invoke a u-turn in livemap. Where does that leave us?

PesachZ wrote: first lets make sure it is reproducible when not at the beginning of a route. To do this you would have to move your start point further back so it is at least several full segments before the U-turn. Then if you can still reproduce it, we will have to wait for a tile update and test again (since the segments were just edited today. If the U0turn still works after that we can try to have staff investigate it, for that we wil need the livemap PL for the route with the uturn in it.

TheLastTaterTot's proposed new page on the mechanism does warn that u-turn prevention can fail when the u-turn is the first segment of a route or re-route. That may have been what happened to the UR, granted, it's hard to tell. However, my livemap route also offers the u-turn, and it starts on the 4th full segment prior to the incoming segment of the u-turn. Is this sufficient distance? When you say "at least several full segments before the u-turn" it appears to contradict the new wiki guidance, which says the mechanism can fail when it's the first segment of a route/re-route. Shouldn't one full segment prior to the incoming segment be enough? In my case it's 4 segments prior to that, and it's still failing. I know you're fully involved in the thread discussing the new page - are there additional undocumented conditions that can cause u-turn prevention to fail?

Thanks for the help/insight - it's much appreciated.

PesachZ wrote: the "one full segment" we know for sure, but we dont know for sure if 2,3,4, or 5 segments, or a specific linear distance has the same effect. If more than 5 full segments still allows the uturn, send the PL and I'll try to ask staff to investigate.

This illustrates one aspect of the wiki I find challenging: it includes those things editors know to be true (or at least, think to be true beyond a reasonable doubt), but omits things that editors are equivocal about, or for which not enough evidence has accumulated, or lacks waze staff confirmation, or whatever. If there is some reason to believe u-turn penalty can fail to be applied on routes that start between 2 and 5 segments away from the incoming segment of the u-turn, can't the warning box in the article state that the penalty can fail to be applied on routes 1 segment length from the incoming u-turn segment, and is thought to possibly fail for 2 to 5, or some indeterminate linear length? At least editors reading the article would become aware of the state-of-knowledge of the limitations of the routing penalty.

Cheers

kentsmith9 wrote: I believe we do include all that we know and to your point I think we have just not thought about adding that particular point into this page. I see no reason why we should not include it once we have enough to confirm how it affects this operation.

Fair comment... I should do well to remember that the wiki is always a moving target. At any rate, if PesachZ says it's definitely more than 1, and possibly up to 5 segments, that'd be definitely worthy of inclusion. Thanks!

Update on the u-turn prevention mechanism failure reported earlier in this thread:

Infrequent but recurrent URs complained of being directed to u-turn here, despite both the median length and the turn angles being within the prescribed guidance. The u-turn was sometimes reproducible in Live Map, with starting point >4 full segments away from the incoming segment of the u-turn.

As a test, the central median was shortened to 9 m, and the angles were adjusted to exactly 90 degrees, as per the voodoo sometimes recommended on the forums - and contrary to official guidance which says that 14 m and 175 to 185 degrees total angle of incoming to outgoing segment should be sufficient to prevent u-turns.

After tile update, I find I cannot reproduce the u-turn instruction in Live Map, despite trying many iterations of start/end points & times-of-day similar to what previously would occasionally give a u-turn. In this particular case, absent any other cause, it seems possible that one or both of these anecdodal remedies were sufficient to kick in the detour penalty. If true, the corollary would be that 14 m median and 175-185 degree total angle did not constitute sufficient conditions to invoke the penalty. Thoughts? Am I missing something obvious?