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Segment Lengths

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In a recent thread I was inspired to collect all the info we have on segment lengths and create a template or whole wiki page on it.

I believe we want to note the following and I would appreciate any other ideas:

* Max length allowed by editor from both initial creation and when connecting segments by removing nodes. (I believe we have seen this in the 10km range; I will do some tests unless someone already has.)
* Max recommended length - Explaining pros and cons of longer or shorter lengths on routing, visual traffic indicators, etc.
* Limit on stretching the length of a short road too far in one edit. Also if it is better to stretch it or draw a new road to preserve the traffic data on a segment.
* Min length
* The affect (if any) from connecting nodes (2 segments) on routing penalties, server load (back-end database management), editor complexity, turn restriction errors, etc. Also cover if it is any different for junctions (3+ segments).

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Post by banished
I asked the maximum segment length question in a face-to-face meeting with Waze in September 2013 and the response was 10km. If there is a need to revisit the question, perhaps we should ask again?

I'll take the action item to do so. It's a particular interest to me -- and the reason I asked them initially -- due to railroad segments which the present wiki says to keep at <=10km (https://wiki.waze.com/wiki/Road_types/USA#Railroad). The answer for railroad (non-routable) segments may not be the same for routable segments, however, so it's worth asking again.
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Post by banished
Segment length follow up: I received an answer from Waze: It's up to 100km. For our purposes that is not effective until we agree to change it in the wiki.

Although I have a good system, it starts to drag if the segment length is over 70km. I don't know if that's my system or the WME, but you may wish to run your own tests in out-of-the way areas so we can arrive at a number that works for everyone.

Segment length was initially a railroad segment discussion. There aren't too many navigable segments that would reach that length (70km), but there may be a few in the Western US/Canada.

I'll open the bidding at 50km.
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Post by bgodette
kpouer wrote:Maybe, and on very long segments, I don't expect a lot of traffic jam as they are not in urban area usually.
There is still my other problem on traffic data on very long segments if the geometry is changed (and also because I don't know what happens with erratic network connections.
WME's backend takes care of recomputing time-slot transit times for any modified or split segments. This is likely why saves involving node removal can take a while.

Incidentally this is something that Cartouche did NOT do. Changes to segment length did not modify transit time, so if you lengthened you'd make routing think that segment was faster, shorten and it looks slower.
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Post by bgodette
kentsmith9 wrote:The net result for routing is no different though. The routing engine will still account for the time change over the entire length of the segment the same as it would for ten 5km segments with the stoppage at the same point.
Routes with fewer segments are preferred by routing over a route with more segments even if the route with more segments seems to save some unspecified amount of time. Some percentage of the secondary route being a faster route is caused by this.
kentsmith9 wrote:However, the net result for the visual will be different. The 50km segment will possibly never show slow traffic when you plot the route and look at the initial traffic. Only later will you run into the stopped traffic. With short segments, Waze can warn the driver of a slowdown of traffic because the segments are shorter and will be detected as different from their average.
FYI we've seen occasional peeks at traffic highlighting in the app showing sub-segment highlighting. Using highlighting as a thin justification for segment splitting is likely to be eliminated "soon".
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Post by CBenson
kentsmith9 wrote:In a recent thread I was inspired to collect all the info we have on segment lengths and create a template or whole wiki page on it.
That's not a public thread.
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Post by CBenson
jasonh300 wrote:I have a segment that is 65000 meters that I've adjusted a number of times with no ill effects. There are no other segments connected to it though.
I have long segments that I can adjust without problem. But when I've tried to create long segments, I've had issues saving.
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Post by CBenson
I find a pro to long segments to be enhanced visibility of traffic due to traffic indication being at (or at least near) the junction where I need to make the decision as to whether to divert to avoid the traffic.

If the freeway segment is cut into smaller segments and I'm about to get on the first segment with no way off of it, I prefer that it be marked as jammed even if the slowness is concentrated at the other end. I really don't care to see where the jam is along a segment I can't exit, as I can only decide to get on it or not. If I'm on the segment, the jam is going to slow me no matter where on the segment it is.

However, I don't encounter many segments over about 7 km on my commute, so this might not really apply to "very long" segments.
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Post by CBenson
kpouer wrote:If a segment is 20km long and there is some traffic jam on 3km, I think it will be hard to detect.
I'm not understanding. If you have a stoppage 1km into a 7km segment, waze can detect that and the segment should turn dark red or black. If the jam doesn't significantly affect the average speed because the segment is so long, then why is the information significant for routing decisions?
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Post by CBenson
When I lose 10 min on a 7 km segment that usually takes me 4 min to travel, waze marks the segment as jammed.

Even on a 20km segment with an average speed of 105 kph, a 10 min delay would almost be halving the average speed.
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Post by doctorkb
jondrush wrote:1m is the minimum length.
Hate to pull up zombie threads, but this one was recently quoted, and felt the need to mention something.

Waze Staff have informed us that segments shorter than 5m actually cause problems for the routing engine.
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