Improper Detour Prevention Mechanism/Algorithm

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Improper Detour Prevention Mechanism/Algorithm

Postby Krixera » Wed Apr 29, 2015 12:06 am

After Waze introduces detour prevention mechanisms, I've noticed many improper/unoptimized routing especially on normal streets. Detour prevention on highways and freeways are logical and fundamental, but when comes to street level it's not appropriate and it has a negative effect by giving longer routings. Take these segments for example: Permalink

If these segments has a width of LESS THAN 16M, U-Turn on these segments will never be allowed unless it's the only route to destination. Why would we wanted that? And do take note sometimes when a driver took a wrong turn, a weird and lengthy U-Turn routing will appear as a result of this mechanism, I have adjusted many of such median to 16m purposely to avoid the detour prevention mechanism(15m median confirm not working and thus 16m is the threshold width).

At many times, to achieve a 16m wide median will mean upsetting the road geometry: Permalink, and it's getting rather annoying to expand each and every normal street segment to avoid the detour prevention mechanism which will actually CONFUSE THE ROUTING SERVER TO OFFER AND EVEN LONGER ROUTE. Thus I hope the routing team will look into this matter which I have summarise as follows:
1) Detour prevention mechanism should NEVER be effective on road type LOWER THAN HIGHWAY, even when ONE of the segment involved in the detour is lower than highway type, ie: ramp-street-street. In short, detour prevention mechanism should never be allowed on street.
2) Update in the wiki on the threshold width of detour prevention mechanism which is actually at 16m but not 15m, and do consider shortening this length if the 1st suggestion cannot be implemented. 10m will be an acceptable length but somehow this rule should not apply on highways where detour mechanism is essential.
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Re: Improper Detour Prevention Mechanism/Algorithm

Postby Krixera » Sat Jun 11, 2016 2:48 pm

It seems my topic here received no attention at all while this algorithm has seriously affected many routings with median less than 16m.

Take for example this UR here which I've raised myself: https://www.waze.com/editor/?env=row&lo ... st=6375432, I'm suppose to be travelling on Jalan SR 8/2 and to expect a Turn left and then Turn Left prompt to get into Jalan Utama: https://www.waze.com/editor/?env=row&lo ... ,165377469. But due to the median here is less than 16m: https://www.waze.com/editor/?env=row&lo ... =143118945, which is a condition being created by Detour Prevention Mechanism but somehow falsely effective on this segment, the routing has bypassed the shortest route and in return offered a LONGER ROUTE which is as illustrated in my 1st permalink above.

Please be noted there are millions or probably billions of segment with median less than 16m. If this algorithm never change/ being revised, there will be countless false routing being created. Detour Prevention Mechanism is meant to be effective on a Highway to avoid dangerous detour but NOT on a normal road like Primary Roads and the road type below. Please revise and correct this algorithm as soon as possible as major false routing has been created in Waze which causes Waze not being able to 'outsmart traffic' anymore.
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Re: Improper Detour Prevention Mechanism/Algorithm

Postby JB15TM » Sat Jun 11, 2016 8:18 pm

Hi. Sorry your first post was not answered. Once they go a few days - and drift to the second page - it's easy to overlook.

The 15 meter cross length is not a Detour Prevention mechanism. It's there for UTurn prevention - mainly for boulevard exchanges where a left turn is allowed, but you want to prevent a U Turn.

The segment length also has nothing specific to do with the physical median width.

If a U Turn is not illegal and is reasonably possible, the median segment can be set to 16m so that U Turn can be routed.

I'll try to look at your actual links when I can get online in WME.


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Re: Improper Detour Prevention Mechanism/Algorithm

Postby JB15TM » Sat Jun 11, 2016 11:46 pm

[quote="Krixera"]It seems my topic here received no attention at all while this algorithm has seriously affected many routings with median less than 16m.

Take for example this UR here which I've raised myself: https://www.waze.com/editor/?env=row&lo ... st=6375432, I'm suppose to be travelling on Jalan SR 8/2 and to expect a Turn left and then Turn Left prompt to get into Jalan Utama


The problem here is that there is no segment mapped in Waze for the turn you expect to make. This has nothing to do with detour prevention or U turn prevention. If a U Turn here is legal, simply add a segment for routing. There is no algorithm problem here.

Also - regarding your original post from last year - I looked at that PL and all segments there are >15m so there should not be any issue here with U Turn prevention. I'm not sure about how the streets are routed as I'm not familiar and the street view is inconclusive. If there is a routing problem there, you need to discuss that with the local editors. But it's not an algorithm problem from what I can see.

Hope this helps.
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Re: Improper Detour Prevention Mechanism/Algorithm

Postby Krixera » Sun Jun 12, 2016 4:35 am

Hi JB15TM,
Thank you for your response. There's a few things I need to clarify here before things went wrong. First, I'm not 100% sure whether this is a Detour Prevention Mechanism effect, or if there's another 'U Turn prevention mechanism' as you have stated. But this effect will be EFFECTIVE as long as the median segment to do a U Turn is less than 16m.
My 1st posting has been long ago and back then these medians which were previously less than 16m had all been extended to 16m by me to bypass this weird mechanism. However, my latest post I'm still retaining the segment length at 15m for anyone to anayse and troubleshoot the problem. The median is always there, it's not missing, so I know not why you've mentioned there's no median there for the routing to work properly. If this so called 'U Turn Prevention Mechanism' has only minor effect, I wouldn't have highlighted it and I'm willing to bypass using my method. But please be noted there are so many segments worldwide which has a length with less than 16m and all u turns routing via such median will ALL BE AVOIDED which results in a longer and ineffective routing. It's not possible to rectify all such medians and correct them all to 16m length, so the best way is to revise and improve the mechanism. A simple guideline to start with is NOT ALLOWING this mechanism to run as long as any segment INVOLVING PRIMARY ROAD TYPE OR BELOW. As we do not need u turn prevention on a normal street.
Furthermore in streets where there are multiple road segments parallel to each other, it's hard or nearly impossible to extend the median length to 16m as it will be made too close to the next parallel segment and causes the U Turn Prevention effect on the next street. I've encountered this problem in the past and to be frank I'm very upsetted to compromise with this U Turn Prevention Mechanism which post NO BENEFITS OR SIGNIFICANCE on Primary Roads and Street AT ALL.
Please do revise this mechsnism and find a smart solution to it soon. Thank you.
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Re: Improper Detour Prevention Mechanism/Algorithm

Postby FzNk » Sun Jun 12, 2016 6:01 am

The segment you linked in your recent post is actually 14.5m rounded up to 15m. There is/was guidance to set median segments to at least 16m to avoid this rounding issue and stretching that segment another meter wouldn't seriously

Changing the guidance in the wiki wouldn't affect how the routing algorithm actually works, it would just make the guidance wrong. You would have to communicate with staff through the appropriate channels to propose the change you're suggesting.
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Re: Improper Detour Prevention Mechanism/Algorithm

Postby Krixera » Sun Jun 12, 2016 7:27 am

Not that I'm not aware of this adjustment but as mentioned some places where there are close parallel roads on both sides, adjustment of such will be tough and it upsets the geometry of the roads, eg: https://www.waze.com/editor/?env=row&lo ... =145263568. In order to compromise to this median, the segment next to the above is being affected by another U-Turn prevention and routing at node B will suggest a U-Turn routing on left rather than on right(even if the routing on right is closer/faster).
And as I said, no editor can rectify ALL AFFECTED MEDIANS and cure this world wide problem. U Turn Prevention is USELESS on normal street. It should be either revised or abolished for normal street. I'm pretty fed up to reply those false routing URs caused by the flaw design of this mechanism.
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Re: Improper Detour Prevention Mechanism/Algorithm

Postby FzNk » Sun Jun 12, 2016 3:33 pm

In most places, the road in front of the businesses wouldn't be mapped separately and Persiaran Raja Muda Musa would just be mapped as two-way. I can see how this could be an issue here, but most of the world is not this tightly packed.

The u-turn prevention has been in place as long as I've been editing and I've not run into a situation that couldn't be fixed by either widening the gap slightly or simplifying the mapping of the roads. Changing this mechanism for the whole world would create issues for all of the mapping that relies on it to prevent illegal/impossible u-turns.
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Re: Improper Detour Prevention Mechanism/Algorithm

Postby KTCAOP » Sun Jun 12, 2016 4:35 pm

Even for roads that tightly packed, the angles could be adjusted or the "Three Segment" rule could be broken as well (though this may have extremely unfortunate consequences in terms of routing). There are three parts of the U-Turn prevention (which should be noted gives a penalty, not 100% restriction) and all three must be fulfilled in order for it to be in place.
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Re: Improper Detour Prevention Mechanism/Algorithm

Postby Krixera » Mon Jun 13, 2016 6:09 pm

FzNk,
Almost every U-Turns on normal streets are legal, especially in housing estates and commecial areas where medians are narrow(<16m). All U-Turn routings are being avoided on such medians for no logical reason. Like I've mentioned many, many times, it's more effective to be implemented on highways only.
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