why no left turn at intersection

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why no left turn at intersection

Postby bz2012 » Sun Mar 24, 2013 1:04 pm

A user asked:
Problem: why not turn left at light from bluebonnet onto airline
Reported on: March 21
https://www.waze.com/editor/?lon=-91.06 ... TTTFTTTTFT
All turns are allowed (except the U turn).
2013-03-24_073940.png
2013-03-24_073940.png (20.62 KiB) Viewed 3955 times
Road types look OK.
Live map shows the same crazy routing that the driver was getting.
2013-03-24_071736.png
2013-03-24_071736.png (22.51 KiB) Viewed 3958 times


I think the intersection had been working.

Questions:
    have recent changes in routing algorithms broken the intersections?
    What is the 'best way' to fix it?
I am tempted to 'add a left turn lane', perhaps as simple as this,
2013-03-24_072001.png
2013-03-24_072001.png (206.11 KiB) Viewed 3959 times
perhaps starting earlier, where the 'left turn only' pavement markings begin, even though the 'best practice guidelines' frown upon such things.

If I KNEW it was a routing algorithm problem and would soon be fixed, I would just leave it as is and mark it solved.
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Re: why no left turn at intersection

Postby CBenson » Sun Mar 24, 2013 4:54 pm

Its a routing algorithm issue.
The live map shows the routing algorithm's fastest route. But waze routes fine if the navigation type is set to shortest.
Bluebonnet.jpg
Bluebonnet.jpg (25.75 KiB) Viewed 3483 times

Thus, I do not believe that any correction to the map is warranted. My understanding of the issue is that with the speed data that waze has, waze has calculated that on average it is faster to take the right/U than it is to wait at the light to make the left turn. Sometimes you can fix this by actually driving the U route so waze gets better data.

I'm not sure that this is considered a "problem" to be fixed, as based on the waze data it seems that it is the fastest route.
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Re: why no left turn at intersection

Postby bz2012 » Sun Mar 24, 2013 5:29 pm

CBenson wrote:Its a routing algorithm issue.
The live map shows routing algorithm fastest route. But waze routes fine if the navigation type is set to shortest.
Bluebonnet.jpg

Thus, I do not believe that any correction the map is warranted. My understanding of the issue is that with the speed data that waze has, waze has calculated that on average it is faster to take the right/U than it is to wait at the light to make the left turn. Sometimes you can fix this by actually driving the U route so waze gets better data.

I'm not sure that this is considered a "problem" to be fixed, as based on the waze data it seems that it is the fastest route.


Hmmmm That makes sense until I take a look at the actual figures.

I would like to know how they compared the two routes and come out with faster for the longer. Something is seriously wrong with their algorithm!

Neglecting time lost making turns, here is what I calculate for time to get to the node where the left turn is made on the short route:

segment 1 (short route) Length: 15 meters
Average speed for segment*
B->A: 20km/h (12.4mph or 5.543 meters/second) = 2.7 seconds
total 2.7 seconds

segment 1 (longer route)Length: 178 meters
Average speed for segment*
A->B: 54km/h (33.6mph or 15.021 m/s) = 11.85 seconds
segment 2 (longer route) Length: 18 meters
Average speed for segment*
A->B: 6km/h (3.7mph) = 10.88 seconds
segment 3 (longer route) Length: 81 meters
Average speed for segment*
A->B: 11km/h (6.8mph) = 26.64 seconds
segment 4 (longer route) Length: 91 meters
Average speed for segment*
A->B: 9km/h (5.6mph) = 36.35 seconds
total 85.7 seconds

85.7 seconds seems quite a bit slower than 2.7 seconds!

I think another possible 'fix' is to make the 'crossover' on the long route a 'parking lot road'.
Any objections to this?
Last edited by bz2012 on Sun Mar 24, 2013 5:34 pm, edited 1 time in total.
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Re: why no left turn at intersection

Postby CBenson » Sun Mar 24, 2013 5:33 pm

But you don't have the data that waze uses to make the calculations. Waze has said that the average speed data available in the editor is not the base data that the routing algorithm uses. Waze keeps data on how long it takes to go each direction at the end of the segment. So waze has data on the difference for turning right compared at least to going straight and left, that you are not accounting for in your calculations.
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Re: why no left turn at intersection

Postby bz2012 » Sun Mar 24, 2013 5:40 pm

Agreed, but right, left, straight (long route) would seem longer than straight, left (short route), especially when the long segments are added in, along with waiting for a chance to make that 'U' turn safely.

Granted, there may be a 'right on red after stop' advantage, at that intersection that we are not seeing.
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Re: why no left turn at intersection

Postby CBenson » Sun Mar 24, 2013 5:43 pm

bz2012 wrote:I think another possible 'fix' is to make the 'crossover' on the long route a 'parking lot road'.
Any objections to this?

I don't think this is a good idea. First, its not really a parking lot road. Second, from a routing perspective, you might as well simply remove it rather than making it a parking lot road. If you make it a parking lot road, I don't think it will ever be used for routing.
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Re: why no left turn at intersection

Postby CBenson » Sun Mar 24, 2013 5:48 pm

I think its likely a combination of:

1)
bz2012 wrote:along with waiting for a chance to make that 'U' turn safely.

As no one likely makes the U, waze likely doesn't have good data on what that wait is, and thus may well be severely underestimating this wait.
and
2)
bz2012 wrote:Granted, there may be a 'right on red after stop' advantage, at that intersection that we are not seeing.

Waze likely does have data showing the right is on average significantly faster than going straight/left.
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Re: why no left turn at intersection

Postby bz2012 » Sun Mar 24, 2013 6:00 pm

CBenson wrote:
bz2012 wrote:I think another possible 'fix' is to make the 'crossover' on the long route a 'parking lot road'.
Any objections to this?

I don't think this is a good idea. First, its not really a parking lot road. Second, from a routing perspective, you might as well simply remove it rather than making it a parking lot road. If you make it a parking lot road, I don't think it will ever be used for routing.


I don't really think WAZE should EVER route people via a 'U-turn' when there is another way to get there. U-turns are dangerous, even when legal, especially when there is no 'left only' lane leading to the U-turn. I believe there is a high incidence of accidents associated with U-turns, in general.

When I drive, I try to avoid making U-turns, even when legal. I would rather go down a side street or into a parking lot to turn around.

I always make 'safety of the drivers' my first priority.
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Re: why no left turn at intersection

Postby Bigbear3764 » Sun Mar 24, 2013 6:12 pm

bz2012 wrote:
When I drive, I try to avoid making U-turns, even when legal. I would rather go down a side street or into a parking lot to turn around.


Don't drive in Michigan. They make you go past the street to make a left, loop around and come back to make a right. Now most busy intersections have a stop light for the Michigan left.





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Re: why no left turn at intersection

Postby CBenson » Sun Mar 24, 2013 6:25 pm

bz2012 wrote:I don't really think WAZE should EVER route people via a 'U-turn' when there is another way to get there.

Ok, but it seems to me that is an argument for removing the segment as U-turns are its only function.
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