Odd Route Around the Block

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Odd Route Around the Block

Postby CBenson » Mon Nov 11, 2013 3:30 pm

I've seen a number of recent complaints that waze is routing around the block when there is no traffic to justify the route.
This morning waze gave me the following route:
OddBlock.png
OddBlock.png (61.48 KiB) Viewed 498 times

Its looks like waze is seeking out the slow streets to route me on. There was no traffic or other delay if taking L St between 7th and 9th when I got there.

Interestingly, this is at the end of a route that was started 50 minutes earlier. One explanation is that at the time the route was created there was some indication that continuing on L to make the left turn was slow. And that even if waze did subsequently receive information that the block of L had cleared, the time savings is not enough to justify calculating a new route.

Waze almost never gets my ETA correct in the morning. It creeps later and later as I drive. I've wondered whether waze gives too much weight to realtime data compared to historic data when looking at roads an hour into a route. However, today is a holiday with atypically light traffic for a Monday morning. Waze clearly took into account the light traffic when calculating my ETA this morning and would have given me much greater ETA if it was using historic data for the typical Monday here.
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Re: Odd Route Around the Block

Postby CBenson » Wed Nov 20, 2013 2:35 pm

All four intersections have traffic lights. Only the turn from 7th to M has a dedicated left turn signal, but it comes at the end of the green for going straight. The one caveat is this is a corner of the new Marriot hotel that is being built for the convention center, so for the past year or so there has been a flagman at the intersection to stop traffic when required to let the trucks serving the construction site enter and leave the site. However, waze takes me through this intersection daily and does not usually send me around the block. The route is usually straight across L and left on 9th. So I'm fairly certain that the historic data shows that it is faster to make the left from L to 9th. Thus, I find it interesting that when I called up the route at home, waze routed around this block 50 minutes into the route. It seems to me that this means that waze has detected a real time slowdown for the turn or for that segment of L and is applying that real time data to the route even though I won't reach the segment for at least 50 minutes.
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Re: Odd Route Around the Block

Postby CBenson » Wed Nov 20, 2013 3:35 pm

What you say makes sense, but this route seems to indicate that waze works otherwise.

The other factor was that this route was on Veterans Day, which is a federal holiday. So the traffic into DC was very light compared to a normal Monday morning. The ETA for my route that morning was less than the normal Monday morning. That route started with an ETA of 46 minutes (so the turn was really only scheduled to be 44 minutes into the route), while the ETA this past Monday was a much more typical 55 minutes. As I don't understand waze to keep a list of national holidays to distinguish Monday November 11 from a typical Monday, it seems to me that the ETA must have been based on the real time data throughout the route for that day. The time doesn't vary that much at the beginning of my morning route. Its the final 5 miles in the city that makes the major difference. If waze was using historic Monday morning data for the final 5 miles I don't see how it could have determined that the ETA would only be 44 minutes on Veterans Day.
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Re: Odd Route Around the Block

Postby Riamus » Wed Nov 20, 2013 1:49 pm

Out of curiosity, how is that left turn designed compared the left turns on the selected route? Stop sign or stop light? I'm just wondering because the highlighting would be based on the segment speed and not on the time it takes to make a turn. If L is a stop sign where you could sit for a while during morning traffic before making the turn, then it might make sense why it routes another way that could have dedicated turn lights. Just a thought. Otherwise, I'm not sure.
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Re: Odd Route Around the Block

Postby Riamus » Wed Nov 20, 2013 2:50 pm

Strange. It may be related to the other around-the-block errors that have been reported lately. Those seem related to some routing bug rather than a map problem or speed problem. I wouldn't think Waze would use the current speed directly when determining a route that is 50 minutes away. Maybe it does, but that doesn't make much sense. I would have expected Waze to look at how speeds are compared to normal currently and use that to help estimate what the speed will be when you get to that point based on how speeds are now compared to normal and then adjusting that to the historical speeds at the time you'll arrive. Kind of along the lines of -- If the speed right now is 5mph under the normal for this time of day and the historical speed for a road you'll be on in 50 minutes is 45mph, then adjust that down to 40mph as an estimate. Of course, that should also scale the longer it will be before you reach the area. So if it's 10 minutes away, it might adjust it down the full amount, but if it's 50 minutes away, it will adjust it by only 50% (2.5mph in this example) and if it's 2 hours away, adjust it by only 5% since current conditions compared to normal aren't likely to still be in effect in 2 hours. Those are of course just random numbers thrown out to give an idea of what I'm talking about. They aren't meant to be actual numbers to use. Maybe that's not a good way to do it, but I think it makes more sense than using current speeds directly if it's that long until you reach the location.
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