[Page Update] Junction Style Guide

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Re: [Page Update] Junction Style Guide

Postby sketch » Fri May 23, 2014 6:57 am

Long-awaited. "Delayed" implies a date has been set and missed.
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Re: [Page Update] Junction Style Guide

Postby qwaletee » Fri May 23, 2014 9:49 pm



Thanks. I guess this one sort-of-is sort-of-isn't truly an interchange. Be nice to mention some of the major interchange types on the main page in the summary section.
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Re: [Page Update] Junction Style Guide

Postby Bigbear3764 » Sat May 24, 2014 12:31 am

qwaletee wrote:


Thanks. I guess this one sort-of-is sort-of-isn't truly an interchange. Be nice to mention some of the major interchange types on the main page in the summary section.

I see what you mean. Someone must have fixed the redirect on it. I searched now and got the 2 results for Junction Style Guide and Junction Style/Interchanges.
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Re: [Page Update] Junction Style Guide

Postby kentsmith9 » Sat May 24, 2014 5:44 am

I also fixed the link from the Wayfinder Glossary entry to the JSG subpage.
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Re: [Page Update] Junction Style Guide

Postby sketch » Fri May 30, 2014 5:10 am

https://wiki.waze.com/wiki/Junction_Sty ... ersections

I have started work on the "split road intersections" section of the intersections subpage.

Including — making that section at all, basically. Before, the entire section was a guide on bowties, which I believe led to the overuse of the bowtie in certain areas. There was 0 guidance on any other way of representing a split road intersection besides with a bowtie — even when U turns are allowed.

Bowties are never necessary at 3-way intersections, or at 4-way intersections where all U turns are allowed or where restricted lefts would restrict any disallowed U turns anyway. I intend to limit their use to only those situations in which they are necessary — because the bowtie is less intuitive, can increase complexity (where a bowtie would require AGCs to suppress MPs and advance instruction timing), and can cause problems (vis-à-vis turn angles creating unnecessary instructions).

I also intend to offer alternative methods to restrict U turns (including the 'diagonals in the box' method).

I'm also trying to keep in mind what might change when Junction Box is introduced — some of the guidance will, I imagine, remain similar to the guidance as to when to use bowties/alternatives, although it will differ slightly (e.g., no need for a Box when all lefts are restricted or when restricted lefts disallow all U turns anyway; use a Box wherever U turns are allowed).
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Re: [Page Update] Junction Style Guide

Postby CBenson » Fri May 30, 2014 10:20 am

I would just note that if the information here is correct, then a plain box intersection has the disadvantage that the timing data for a straight movement is not distinguished from the timing data for a left turn. There is some question as to how much this contributes to right/U/right routes in place of straight through routes. Theoretically, neither the bowtie nor the diagonals in the box method suffer from this problem.

I acknowledge this is highly speculative as it depends on how the data is collected and assigned to small segments is small areas.
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Re: [Page Update] Junction Style Guide

Postby qwaletee » Fri May 30, 2014 12:58 pm

CBenson wrote:I would just note that if the information here is correct, then a plain box intersection has the disadvantage that the timing data for a straight movement is not distinguished from the timing data for a left turn. There is some question as to how much this contributes to right/U/right routes in place of straight through routes. Theoretically, neither the bowtie nor the diagonals in the box method suffer from this problem.

I acknowledge this is highly speculative as it depends on how the data is collected and assigned to small segments is small areas.


A plain box intersection as opposed to what? A bowtie with a single convergence point? The box breaks off the right from the left and straight through. The only problem might be the chunking of left together with other traffic, at a left turn restrictive signal.
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Re: [Page Update] Junction Style Guide

Postby qwaletee » Fri May 30, 2014 1:08 pm

sketch wrote:https://wiki.waze.com/wiki/Junction_Style_Guide/Intersections#Split_road_intersections

I have started work on the "split road intersections" section of the intersections subpage.



The following sentence is very awkward:
When a U turn must be restricted, but both of the left turns that make up that U turn are allowed on their own, follow the guidance in Avoiding U turns below.


It sort of leads you to other sections, but doesn't really, as it is not specific enough. The compound phrasing might also be confusing to a new reader. Instead, why not have a short intro sentence or three describing what we are talking about, and why there might be problems. Follow that with a table of problem/solution pairs that link to individual solution sections titles.

Next: We're going to deep in the number of headings. We're already at =====, and some of the sections at that level are really subsections (I think) in structure. For example, I would think that U-turns would be a heading that explains the problem and includes subheads for bowtie and bypass connectors (aka, slanty left tpage. a separate urn lanes). Instead, they are forced to be at the same level because we've gone this deep. Some restructuring at the higher levels might be warranted, or a breakout into.

Finally, the bowtie section seems to be an accidental pastiche of content form bowtie and H intersections. They don't belong together and jump back and forth between describing the two veyr different intersection types.
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Re: [Page Update] Junction Style Guide

Postby CBenson » Fri May 30, 2014 1:16 pm

qwaletee wrote:A plain box intersection as opposed to what? A bowtie with a single convergence point?
Yes. A plain box as opposed to either a bowtie with a single convergence point or a box with diagonals with the three segments (one for each direction) connected to the segment on which you wait for the light.

qwaletee wrote: The box breaks off the right from the left and straight through. The only problem might be the chunking of left together with other traffic, at a left turn restrictive signal.

Exactly.
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Re: [Page Update] Junction Style Guide

Postby PesachZ » Fri May 30, 2014 2:41 pm

CBenson wrote:I would just note that if the information here is correct, then a plain box intersection has the disadvantage that the timing data for a straight movement is not distinguished from the timing data for a left turn. There is some question as to how much this contributes to right/U/right routes in place of straight through routes. Theoretically, neither the bowtie nor the diagonals in the box method suffer from this problem.

I acknowledge this is highly speculative as it depends on how the data is collected and assigned to small segments is small areas.

Based on my under standing of the turn delay recordings, and how it is affected by these small segments it would not cause the right-u-right vs. straight. Let me explain my understanding of how it works, and then you can correct me where I am wrong.

Waze keeps track of how long it takes a vehicle to traverse a segment, to move from the beginning of one segment to the beginning of the next segment and continue past the junction. Waze understands there might be a delay in transitioning to the next segment, say for a traffic control device, or waiting for passing traffic to make a turn. Waze accounts for these transition delays by including the time for the transition delay with time it takes to traverse the originating segment (s-in). So the recorded time it takes to pass over this segment includes the time you have to wait at the end of this segment before you start driving across the next segment.

When traffic leaving the originating segment has more than one destination segment (more than one option for s-out) then waze will keep a separate time record for the originating segment corresponding to each of the options leaving the junction. A simple 4-way with 2-way roads then will have travel 3 options when you arrive at the junction, and Waze will record 3 separate travel times for the originating segment, one for traffic ultimately ending ending up on each of those three connected segments. In this way, if there is a longer delay for left turning traffic, Waze can acount for that. It works because Waze knows that traffic from the originating segment which continued straight to the next segment had a traverse time of x + a delay of y, which is shorter than the left turning traffic which had a travel time of x + a delay of z.

A caveat to this system arises when there is a short segment before the junction where the turns are made, and the traffic line waiting to make that turn backs up past the short segment to the segment behind it. The transition delays are still being properly recorded for the short segment (in the intersection box) immediately prior to the turn, but not for the longer segment before it (the street approaching the intersection). The longer segment now only has one option for s-out at the junction between it and the short segment, so Waze only calculate one transition time for that long segment, even though some of the traffic on this long segment is being held up because of the turn delay after the next (short) segment, and other vehicles are moving through freely. The average speed of this longer segment for straight through traffic is now being represented as much slower than it is in reality because Waze is not maintaining separate records (since it only has one exit at the junction). This will affect routing on the long segment, and may cause an alternate route to be chosen for traffic traveling straight through the junction.

wiki wrote:To understand this problem better, consider if we add a short Seg8 between Seg7 and Jnct4. Let's say the traffic exiting Seg10 backs up all the way to Seg7 (easy enough, since Seg7 is short). Because Seg7 only has a single exiting segment (Seg8), the routing server is only able to collect a single average speed — it can no longer distinguish traffic by where it is going after Seg8. Now the through traffic going to Seg9 appears to Waze to slow down through Seg7, even though it doesn't in reality. At a minimum this causes an incorrect ETA for routing, and it might actually cause traffic to be rerouted unnecessarily, and less optimally, through another route. Hence if there is a chance that traffic that goes in different directions at a junction experiences different congestion, keep the segment before that junction long.


This will not cause a Right-Uturn-Right though instead of a left unless the time it takes to complete that maneuver is less than the time it would take to pass through the intersection from the beginning of that short segment and turn left (a very short time). If the situation is such that a right-u turn-right is faster than a left, it would be suggested even without the short segment in the mix.

On a side note, if this is correct that
Waze will penalize a route with two left turns in less than 15 m (50 feet) in right-hand traffic jurisdictions
which is being discussed here, being meticulous about the angles in a simple box type (90 degrees) intersection will, in itself, prevent U-turns, and allow the lefts if necessary.
Last edited by kentsmith9 on Sat May 31, 2014 2:44 am, edited 1 time in total.
Reason: Fixed wiki quote formatting
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