[Academic problem] 8 way intersection without roundabout?

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[Academic problem] 8 way intersection without roundabout?
Okay so, as the title suggests, I came across an academic question which annoys me a bit
Basically, I wanted to implement an 8 way intersection, where you would have (rotational) symmetry AND no roundabout to avoid throughput problems. After thinking about it a little bit, I think this intersection necessarily implies to have a roundabout OR that you would need a ridiculously enormous intersection to avoid rails merging together on some key spots. Since I didn't have the courage to try and implement this ridiculously large intersection, my academic problem would be: what would be the most compact intersection that verifies the imposed conditions? Maybe if some of you work in maths, you could use your knowledge of topology to answer this, who knows?
I just think it could be pretty interesting to submit this problem here, I'd be quite curious about the solutions people may come up with on this forum, so here it is!
Basically, I wanted to implement an 8 way intersection, where you would have (rotational) symmetry AND no roundabout to avoid throughput problems. After thinking about it a little bit, I think this intersection necessarily implies to have a roundabout OR that you would need a ridiculously enormous intersection to avoid rails merging together on some key spots. Since I didn't have the courage to try and implement this ridiculously large intersection, my academic problem would be: what would be the most compact intersection that verifies the imposed conditions? Maybe if some of you work in maths, you could use your knowledge of topology to answer this, who knows?
I just think it could be pretty interesting to submit this problem here, I'd be quite curious about the solutions people may come up with on this forum, so here it is!
Re: [Academic problem] 8 way intersection without roundabout?
You need to define this better. Is a 4way intersection acceptable? How about a 3way intersection? The highest throughput intersections use only side merges and lane swaps, and it indeed results in a ridiculously enormous intersection.
Re: [Academic problem] 8 way intersection without roundabout?
May I introduce you to a forum post that analyzes and compares many different intersections?
viewtopic.php?f=194&t=46855
viewtopic.php?f=194&t=46855

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Re: [Academic problem] 8 way intersection without roundabout?
A roundabout increases the throughput
A basic intersection only allows one train at a time which is the worst you can have.
I think you should reorganize your rail grid just to make the need of a 8 way intersection obsolete.
my complete base is one big roundabout. Trains barelly have to stop.
For example: enough space to let a train speed up before merging in.
When all trains go in one direction there are almost no intersections.
A basic intersection only allows one train at a time which is the worst you can have.
I think you should reorganize your rail grid just to make the need of a 8 way intersection obsolete.
my complete base is one big roundabout. Trains barelly have to stop.
For example: enough space to let a train speed up before merging in.
When all trains go in one direction there are almost no intersections.
Re: [Academic problem] 8 way intersection without roundabout?
Simplest thing I can think of is to invert all of the "diagonal" lanes (flip half of the roads between left and right hand drive), join the inverted lanes with the thenaligned lanes on either side (either merge or run them alongside), and feed it into your choice of 4way intersection (might want to base it on an intersection which uses twice as many lanes as your network and which incorporates lane switching and turnaround).
Re: [Academic problem] 8 way intersection without roundabout?
From what has been measured in the topic seePyou linked, it's exactly the contrary, roundabouts seem to be amongst the worst alternatives.
Koub  Please consider English is not my native language.
Re: [Academic problem] 8 way intersection without roundabout?
He is talking about the whole train system being one giant loop. Not a cross that uses a roundabout at its core.
With one big giant loop the throughput is limited by the number of trains you can put through a single rail line. The merging costs you some more in case there is contention and a train needs to break. But still that's often more throughput than even a single crossing has.

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Re: [Academic problem] 8 way intersection without roundabout?
What I meant by this, is that if you merge some exit tracks, then applying a rotational symmetry would result in a roundabout inside the intersection. For example, let's say we work on the West exit. Then, it would be quite natural to merge the tracks coming from SE, S and SW. But then, if you apply the same scheme on the exit to the North, East and South, you would have a roundabout at the center of the intersection, allowing the possibility of a Uturn for your trains. I'm not sure if I am clear by saying this, but maybe i'll post a picture to illustrate this later.
Of course 4ways and 3ways are acceptable, but I was just playing around with an 8ways intersection. Then, I wanted to take it a bit further and tried to optimise it a little, so I wanted to avoid having a roundabout inside the intersection. I did not work on this for too long, but I thought it'd b interesting to see if someone could come up with an 8ways intersection without a central roundabout!
Yes I have been reading this thread for quite a while now, and even used the throughput tester map for some of my designsseePyou wrote: ↑Sun Apr 14, 2019 10:48 pmMay I introduce you to a forum post that analyzes and compares many different intersections?
viewtopic.php?f=194&t=46855
That's an interesting idea, maybe I'll try something with it later!Eketek wrote: ↑Mon Apr 15, 2019 8:22 amSimplest thing I can think of is to invert all of the "diagonal" lanes (flip half of the roads between left and right hand drive), join the inverted lanes with the thenaligned lanes on either side (either merge or run them alongside), and feed it into your choice of 4way intersection (might want to base it on an intersection which uses twice as many lanes as your network and which incorporates lane switching and turnaround).
I really don't want to be pedantic, but that's not really the point of my thread. First, (local) roundabouts have a lower throughput than intersections, and basically that comes from the fact that you increase the number of paths crossing each other. Also, basic intersections do not allow only one train at a time if you make the signals correctly!JimBarracus wrote: ↑Mon Apr 15, 2019 6:40 amA roundabout increases the throughput
A basic intersection only allows one train at a time which is the worst you can have.
I think you should reorganize your rail grid just to make the need of a 8 way intersection obsolete.
my complete base is one big roundabout. Trains barelly have to stop.
For example: enough space to let a train speed up before merging in.
When all trains go in one direction there are almost no intersections.
Finally, I generally use only 4ways or less in my train networks, but I was just having fun by trying to design a nice 8ways intersection.
However, the idea of the global roundabout is quite nice, but I think it's not very different from the popular grid design and I don't often implement this because I don't find it super interesting. It's very efficient, but a bit boring (in my opinion of course).
Re: [Academic problem] 8 way intersection without roundabout?
Only problem with having a roundabout inside the cross is with trains longer than the size of the roundabout. So lets assume you want your 8 way intersection to be able to handle L*128+C*1024 trains. A roundabout would allow trains to make a 270° turn and crash into them self.
That said I think I only just got what you mean by 8 way intersection. It's no 8 parallel tracks but you want (one?) tracks coming an going from the 4 major and 4 minor compass points. Right?
That said I think I only just got what you mean by 8 way intersection. It's no 8 parallel tracks but you want (one?) tracks coming an going from the 4 major and 4 minor compass points. Right?
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Re: [Academic problem] 8 way intersection without roundabout?
https://mods.factorio.com/mod/entitysymmetrymrvn wrote: ↑Sun Apr 21, 2019 8:43 pmThat said I think I only just got what you mean by 8 way intersection. It's no 8 parallel tracks but you want (one?) tracks coming an going from the 4 major and 4 minor compass points. Right?
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Re: [Academic problem] 8 way intersection without roundabout?
This seems straigth forward:
I cann see no way a train could turn around.Re: [Academic problem] 8 way intersection without roundabout?
Nice! Very elegant.
Problem: you cannot make a hard right from the cardinal directions(0 to 315, 90 to 45, 180 to 135, 270 to 225).
It looks like an easy fix.
Also very interesting...alienwombat wrote: ↑Tue Apr 23, 2019 4:02 pmThis seems straigth forward:
I cann see no way a train could turn around.
Problem: train cannot turn 90 degrees from 45, 135, 225 and 315.
Signaling the additional turns might be difficult.
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Re: [Academic problem] 8 way intersection without roundabout?
The general pattern for designing a highthroughput intersection seems to be:
For each incoming line:
1 branch off separate tracks for each direction it could go to (normally 3, here 7)
2 provide a buffer
3 go to destination while crossing a minimum number of other tracks
4 provide a buffer
5 merge
I see no reason why that wouldn't work here? Of course, why on Nauvis anyone would ever want such a thing is a different question...
For each incoming line:
1 branch off separate tracks for each direction it could go to (normally 3, here 7)
2 provide a buffer
3 go to destination while crossing a minimum number of other tracks
4 provide a buffer
5 merge
I see no reason why that wouldn't work here? Of course, why on Nauvis anyone would ever want such a thing is a different question...
Re: [Academic problem] 8 way intersection without roundabout?
Why would you even need an 8way intersection. Any situation that requires something like that is inherently flawed.
You should never get yourself into a situation where you need more than a 4way intersection and if you really want a hardcore trainbased megabase then you might even think about avoiding 4way intersections too and only go for 3way intersections using a honeycomblike pattern where only 3 egdes meet. That is my advice with experience in civil engineering and urban planning.
But apart from that I have posted one of those monstrosities above years ago because someone else had the same idea but it obviously is useless.
You should never get yourself into a situation where you need more than a 4way intersection and if you really want a hardcore trainbased megabase then you might even think about avoiding 4way intersections too and only go for 3way intersections using a honeycomblike pattern where only 3 egdes meet. That is my advice with experience in civil engineering and urban planning.
But apart from that I have posted one of those monstrosities above years ago because someone else had the same idea but it obviously is useless.
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