
MultiCross Series High-Throughput Mix-and-Match Rail Junction Blueprints by Tallinu

1. Introduction and General Information
2. Included Design Variants
3. Assembly Instructions
4. Construction Tips
5. Links, Feedback, Credits


1. Introduction and General Information

The MultiCross series is intended for situations in which a "normal" or "compact" junction just doesn't cut it. This is what you use when you want to get as many trains as possible from point A to point B, C, or D, quickly and efficiently, and are willing to build a bigger junction to do it. If you have never seen a traffic jam or a deadlock, you probably don't need the MultiCross. But if you see trains stuck on the main tracks, waiting for other trains to get out of the way, or if you are considering installing additional lanes of track in the hopes of speeding up slow traffic, the MultiCross may be what you need!


These junction blueprints are provided in a modular, "some assembly required" form. This has several great benefits:

First, it's a lot easier to place one quarter of a large blueprint at a time than it is to accurately place something twice as large in every direction, even if you are using a mod that lets you zoom out farther than normally allowed (and zooming out too far can really drive framerate into the ground on slower systems).

Second, I've designed all of these in such a way that you can "mix and match" different variants of the design to form a customized junction where each cardinal direction has as little or as much buffering and throughput optimization as needed for the amount of traffic it's expected to deal with. For example, if you have a busy main line going through east to west with some small outposts to the north and south, you can use the longer, higher-throughput segments for the east and west and use the smaller segments for the north and south.

Third, storing the blueprints this way avoids a great deal of redundant data, making the blueprint strings much shorter, and thus nearly 4 times faster to transfer in multiplayer games, compared to a large fully-assembled junction.

These blueprints are all available in both right-hand-drive and left-hand-drive versions. There are a few small, minor differences in track positioning in some cases due to awkward limitations on where signals can be placed, but these are intentional, and all versions have been tested and optimized as much as possible.

I've created rescaled versions of many of these designs, sized for use with trains of different lengths. Make sure that the buffer size of all the segments you use is sufficient to hold the longest trains running on your network. There is one blueprint book for each train length, so that you can simply copy the correct book from your library and have all the variants intended for trains of that size available in one place, ready to be assembled as you see fit. If the posted blueprints don't include a version long enough for your trains, expanding them is relatively straightforward, as long as you cut and paste in the right spot so that the chain signal exit blocks are made long enough. (Expand from the middle of each buffer zone, to avoid duplicating the wrong signals. Compare the resized versions I've created.)

The track spacing on the entrance and exit lanes is one tile wider than the often-seen "minimum swerve" spacing (which has two empty track tiles in between the lanes instead of three). Some people may find this awkward but it has significant advantages for signal placement within a junction, allowing for a more efficient design. If you typically use a different track spacing, you can connect to the junction using a short diagonal lead-in or line up one track and have the other do a zig-zag to move it over the appropriate amount. (Or make both of them zig-zag so they match!) Trying to change the spacing of these blueprint designs is not recommended -- a lot of work went into optimizing their layout and signal placement, and a lot of redesign (and in some places, a lot more track) would be required. Matching the increased track spacing or using the adapter methods I just described would be much easier, and the former doesn't even cost more track pieces (except for weird situations, perhaps).

The blueprint titles in-game begin with a short four-part string which provides all of the important details in one place. Here's a breakdown of the meaning of one example string:

MC 2-L-6

MC: Variant type (MC, MX, TC, TX, MS)
2: Number of lanes (the total number of entrance and exit tracks in each direction)
L: Left-hand-drive (R: Right-hand-drive)
6: Buffer size, in this case it would be meant for trains that are up to six cars long (remember to count all locomotives too)

When combining different variants together, it is important that only the first two-letter part is different. Be careful not to accidentally try to combine LHD and RHD versions in the same junction, for example, and it should be obvious by looking at them that 2-lane and 4-lane versions would not work together. And while it's possible to combine pieces sized for a different number of cars, you would have to be absolutely certain that longer trains couldn't possibly try to use the section with the smaller buffers to avoid possibly triggering a deadlock or a temporary jam. Factorio's trains are known for occasionally doing the unexpected no matter how careful you are, so I recommend avoiding that temptation. (The MS variant is a special case with its own rules, but more on that in its description.)


2. Included Design Variants

The four main blueprint variants are described here in order of increasing size and potential traffic throughput.


MC: MultiCross

The basic model. This is the smallest, and "slowest," of the buffered MC variants. Even so, a junction built from four of these will get far higher throughput than almost any other four-way junction with the same number of lanes, especially a "compact" design. Maximum throughput under heavy traffic load caps out at a little below the theoretical limit imposed by the rate at which stopped trains will merge onto a single track without circuit-network assistance. (This rate is determined by a train's length and acceleration, and is unrelated to junction design, as long as signals are placed properly. More on that in the Tips section.)


MX: MultiCross Expanded

This is an extended length variant with an extra buffer zone that helps smooth out traffic flow through some of the crossings. This results in a maximum throughput under heavy load which is typically very close to the maximum merge rate (without circuits). If there are a lot of trains making turns as well as going straight, it may improve throughput slightly. Otherwise the MC is probably sufficient.


TC: TurboCross

This is a version of the basic MultiCross with extended exit lanes incorporating combinator circuits to intelligently manage the signals. This "Merge-O-Matic" system significantly improves the number of trains able to merge onto the exit track in a given amount of time, resulting in noticeably higher throughput than either of the first two variants.

The combinators do need power to function, but make sure you don't accidentally link any circuit wires you may be running along your power network to the the red and green circuit wires running along the power poles used by the merge manager. They need to remain an isolated system to function properly. (Crosswiring two MoM systems causes both to stop working.)


TX: TurboCross Expanded

Adding the Merge-O-Matic system to the expanded variant results in an even higher maximum throughput, well above the limit for unassisted "dumb" train merging. If you have the room and expect the majority of a junction's traffic to enter and exit in a certain direction (or directions), this variant will definitely ensure that any slowdowns are not a result of limited junction throughput. Even the much-praised simple T junction can have trouble keeping up with this beast under heavy traffic loads. If all your ore from all your outposts comes in from two or three different directions and enters/leaves your base via the fourth, for instance, this may be the traffic solution you need.


MS: MultiCross Stub

Read this carefully before using!

This is a small, unbuffered junction segment for use only in junctions where one or two directions (at most) will have extremely limited traffic AND where the connected tracks won't fill up with trains even under worst case scenarios. Using too many of these or in the wrong places can result in significantl loss of throughput across an entire junction, similar to the kind of traffic problems found in compact junctions.

Unlike the other variants, since these are unbuffered, you MUST ensure there is enough track after the exit signals for an entire train to stop without its rear end blocking parts of the junction behind it. Otherwise a train taking this exit could block all through-traffic. This is not a problem with the other variants because they include buffers before the final exit merge and have chain signals preventing trains from deadlocking the junction, but with this one you must provide your own buffer after the exit.

Also, since this doesn't have any buffers, there is no need to have different versions for different train lengths, so only one set is provided in its own separate blueprint book. You can copy them into whatever book(s) you use most if you want easier access to them. I've avoided duplicating them in each book here to avoid redundancy and keep blueprint library size minimized (which, as I mentioned, can be important for using blueprints in multiplayer games).

Finally, if you have two stubs in the same junction, I do not recommend setting up any train routes that enter through one and exit through the other. Any traffic coming in from or exiting out of a stub should also pass through a normal buffered section (even just a basic MC) to avoid slowing down other traffic or increasing the risk of over-capacity deadlocks. You can probably get away with three stubs if the junction is a dead end (leading to, say, three different outposts near a lake that you never intend to landfill), if traffic is light and trains don't bounce between all of them before returning. But unless there's a pretty steady flow of traffic, a MultiCross of any sort may be serious overkill if you'd be using that many stubs.



3. Assembly Instructions

To assemble, select the desired blueprint and place it so that the central crossing (the "#" grid at one end) is positioned where you want the center of the junction. Measuring and marking it ahead of time may be helpful. Be careful not to use anything which would block the placement of the signals.

Then select the next blueprint variant (if you're using a different one), rotate it, and place it so that the grid overlaps and the curves connect (you may need to point very close to the edge of the screen for the vertical orientations). Do the same for the third and fourth parts.

If using any TurboCross segments, ensure that power reaches the medium poles connecting the combinators. No big power poles are included in the blueprints because everyone seems to have their own preferences for how to place them.

If you aren't sure what you're going to be building in a certain direction, it is perfectly acceptable to leave one or two sections out and add them later. The remaining two or three parts will function just fine on their own!


4. Construction Tips

Since both the entrance and exit lanes for the main four variants (but not the MS Stub) are fully buffered, there is no need to leave additional room for an entire train between this and another attached junction or intersection. This is true even when the other junction is something unbuffered like a standard compact T (three-way).

Also, when trying to maximize the number of trains that can travel along a single track the way these junctions are designed to handle (particularly the TurboCross), it is best to make signal blocks relatively small so that trains can follow each other more closely. A train moving at top speed on rocket fuel leaves around 58 to 60 empty track tiles ahead of it, at a minimum. If it can't reserve that much space, it slows down to keep its stopping point from moving past a red signal. This means that the length of the longest block the trains must pass through is effectively added to that empty track length. In other words, longer blocks force moving trains to space themselves out more, which lowers the maximum throughput of that track.

For high traffic areas, I like to place a signal every seven track segments (approximately), which is the exact amount of space taken up by two rail cars (on horizontal or vertical track at least). Fourteen would also be reasonable, especially if you use longer trains, because the stopping distance they reserve ahead of them doesn't seem to change with train length. These are short enough blocks that a train's stopping point will be relatively close to the train ahead of it, allowing more trains to occupy that length of track at the same time.

(You can turn on a debug option to display a train's stopping distance. This shows a red circle marker which advances as the train accelerates and stops when it begins slowing down. It's an extremely handy diagnostic tool, and fascinating to watch on a Merge-O-Matic, too!)

Finally, if your stations or other junctions leading to the MultiCross simply aren't sending trains fast enough because the track merges leading to it are limiting traffic throughput, it's possible that you won't need or be able to utilize the full capacity of anything more than the basic MC or MX designs. If you're trying to get trains out of several dropoff stations quickly, my Merge-O-Matic may be of use in getting them back onto the tracks leading to the rail network more efficiently. They are tweaked slightly based on the length of train they are expected to handle, so try to copy one out of a TurboCross version that matches your train length.

I hope to post blueprints and detailed instructions for using and adapting them to your needs at some point, but in brief, there's a master unit which controls everything and has the number of lanes it's managing programmed into one of the combinators, and each separate lane has a constant identifying which lane it is. If an expected lane is missing or has the wrong ID number the system will simply stop due to the lack of a response from that lane, and adding higher numbered lanes without adjusting the master unit will mean those lanes simply never get a chance to go.


5. Links, Feedback, Credits

Thank you for your interest in MultiCross series blueprints! Feedback or questions can be sent to me via private message to Tallinu on the Factorio forums -- this link should get you a message window, if you're logged in:

https://forums.factorio.com/ucp.php?i=pm&mode=compose&u=7876

You can find all of these blueprint strings, and any that I finish making in the future, at the following location:

https://drive.google.com/drive/folders/0B-WyBIeg5M4tMTY2ZmJ0NDdVMjQ

If you wish to share these blueprints with others, that's wonderful! Please do so, but I'd appreciate it very much if you'd provide this link to the originals, even if you are sharing modified versions, so that they can easily find any updates, new blueprints, or these instructions. Thanks!

And if you haven't visited Aaargha's four-way junction testing thread, or have any interest in learning more about junction design, or looking at actual empirical test data regarding your favorite junctions, or if you just want to see some interesting designs (and how well, or amazingly bad, they perform), or if you want to run your own tests and experiment with his incredibly useful throughput benchmarking system, please feel free to visit his thread here:

https://forums.factorio.com/viewtopic.php?f=194&t=46855

These junction designs would not exist without Aaargha's work collecting junction designs and providing the testing platform that I used to develop them. Inspiration came from a number of sources found there in addition to my own prior work. My "Cross" and "Windmill" junction designs were the top two test scores in the two-lane junctions list when I first found the thread (someone had sent him links to my imgur album). but combining ideas from those with the patterns found in some other junctions, particularly the crossing and buffering pattern found in the much larger 8-lane "Flower Mk 3", is what eventually resulted in the MultiCross.
