Comments Needed: 3-Way Junction Design.

[AussieNightcrawler]

Posted this in here, thought that it relates to TTD in general and not a specific version off.

I have been using these designs myself and thought that I would share them, there are 2 track and 4 track version, with and without PBS (Path Based Signals), not real sure what junction you would call them, I took the Half Cloverleaf junction and modified it so that trains did not 'loop' around.

Pros:
Handle large number of trains.
Traffic jams unlikely.
2 track version is cheap enough to build.
Choice in which path to take. (Trains can make a choice of which track to go if one way is blocked)

Cons:
Hills to climb.
2 sharp turns.
Bridge(s) to cross.
Tunnels increase train spacing.
Large area needed.

Like I said, comments welcome.

[AussieNightcrawler]

Sorry, only 3 attachments per post, so post 4 track version here...

[Benny]

I wouldn't say that that junction can handle a lot of trains.. Put that on the cons list instead.

[planetmaker]

Especially the 2x2-track version certainly does not have a 'high capacity'. Rather:
con:
a) cross-over of tracks, thus a train going in one direction will block the other
b) join before split
c) short branches, a train having to wait at a join can block other directions
d) Because of a), b) and c) follows: jams highly likely
e) low capacity simply follows from a), b), c) d) and the slow curves

But also the single track version has the join before split, thus jams are inevitable, reducing capacity a lot.

I can recommend to look through our server archives and the games there a bit. There are numerous examples of hubs which should at least address the join before split problem, but usually also the long signal distance due to bridges / tunnels and the lack of curve speed.

[AussieNightcrawler]

Sorry I disagree about jams, I have never had any traffic jams using these junctions, even with networks running 200+ trains, reason why is due to the 'alternative' route, through the tunnels, I have seen trains when faced with a red light will use the tunnel to get to where it has to go. That's what they are there for, you could remove the tracks which join at the center if you think they will cause jams, but I left them there as I have never had any problems so far.

The tracks in the center are the only 'join before split' in the junction, the only problem I have is slowing to climb hill(s) and the bridge.

[planetmaker]

have never had any traffic jams using these junctions, even with networks running 200+ trains

Then try that junction in a place where the junction is really used and all incoming tracks are nearly full (train separation = 0.5 train length for train length ~5 tiles). I've built myself quite a few and seen many more different junction designs in now nearly 150 public server games:
The train count in a network is no indicator, if the junction is hardly used Also inferior junctions work well for low, sometimes even medium traffic but fail, if the load is >~80% of the line capacity. The shown 2x2 version will fail big time.

EDIT: Approx 80% capacity is the train density shown here: http://wiki.openttdcoop.org/images/1/1e/PSG115.png or see possibly http://wiki.openttdcoop.org/File:Coop_a ... n_2108.png and http://wiki.openttdcoop.org/images/2/2c/ProZone10.png for > ~70% Replace those hubs with your design and see yourself, games found at http://wiki.openttdcoop.org/ProZone:Arc ... mes_1_-_10 (last entry) and http://wiki.openttdcoop.org/PublicServer:Archive (games #115 and #47)

[AussieNightcrawler]

Already being used...

There is a section on one of my networks that handles passengers, mail, valuables, ore, wood, steel and goods, there are 11 of the 2-track versions fairly close together, now as I said, you can remove the join/split in the center of the junction if you wish, and I have on a few to force the trains to use the tunnels. I have added an extra track to help improve hill climbing too. Numbers? Passenger/Mail trains are hard to keep track off, but at a guess about 20 - 25, Valuables only around 10. Wood about 16, Steel about 21, Goods about 22, and Ore about 20.

I do not know exact numbers, the game is now at the year 2334, there are 1,223 trains running around, I was using the Ultimate 3-Way junction: http://wiki.openttd.org/Ultimate_3-way_junction, but found that the tunnels on the mainline was slowing everything down to a crawl, so I changed them to the ones above.

Maybe I am using the Maglevs too so I do not see any problems with the junctions, they are fast enough, the PBS makes a difference too.


Have fun..

[planetmaker]

I do not know exact numbers, the game is now at the year 2334, there are 1,223 trains running around, I was using the Ultimate 3-Way junction: http://wiki.openttd.org/Ultimate_3-way_junction, but found that the tunnels on the mainline was slowing everything down to a crawl, so I changed them to the ones above.

Well, people can call it how they like in the wiki. As presented there, it's a nice one, but without doubling the tunnels it's definitely not "ultimate" by my standards Also it depends upon train length.

[AussieNightcrawler]

I am using 7 tiles train length. This is the alternative that I mentioned, "remove the join/split from the center of the junction", you can see this is done in the screenshot attached. This junction handles the main goods line, the exit from the station is just below it, so this junction is the very first junction to see traffic from all trains that service all towns north. If there was any "big time fail" then this is where it would be visible straight away.

You can see that the join/split has be removed and another bridge added.