https://i.redd.it/cldphif2trt31.gif
PART 1: TAKE A SEAT (PLEASE READ)
"Many short trains, or a few long trains, that is the question"
― Every Factorio engineer at some point.
I've recently decided to tackle this important question by taking some time to make a workbook (link at the bottom of this post) simulating trains of different configurations traveling for 40,000 ticks (about 11 minutes), so that I could interpret the results.
Some caveats you should know about:
- I did not account for time spent breaking.
- I did not account for time spent at loading stations.
- The simulation doesn't work for severely underpowered trains (too few locomotives pulling too many wagons).
- The given values are theoretical.
Post breakdown:
- Part 1: introduction.
- Part 2: my process.
- Part 3: recommended train configurations.
- Part 4: conclusion.
You may jump to part 3 if you're only here for the recommended configurations, but it is strongly advised to first complete the exercise in the introductory part in order to fully grasp the concepts discussed.
Untangling headphones (please read)
To make sense of this post, you need to understand these 4 crucial concepts: operation, throughput, fuel efficiency and throughput density:
- A train in a pull operation has front locomotives at one end only; while a train in a top and tail operation (erroneously referred to as a double headed train by some players) has front locomotives at both ends, allowing it to reverse.
- Throughput is the rate at which items are being moved. If you play Factorio, you know what this means, so I won't insult your intelligence by explaining further. Just make sure to remember that for trains, throughput decreases with distance.
- Fuel efficiency is the quotient of throughput divided by the number of front locomotives.
- Throughput density is the quotient of throughput divided by rolling stock; rolling stock being the sum of locomotives and wagons forming the train. Throughput dense configurations allow you to move more stacks with less tracks. In case you're still confused, here's an example (values are fictional):
1 1-3 train travels for 2 km and reaches a throughput of 80 stacks/min.
2 1-1 trains travel for 2 km and reaches a throughput of 60 stacks/min.
The 1-3 configuration has a throughput per rolling stock of 80 / (1 locomotive + 3 wagons) = 20 stacks/min, whereas both 1-1 trains have a throughput per rolling stock of 60 / (1 locomotive + 1 wagon) = 30 stacks/min, making them less fuel efficient but more throughput dense. You can also visually see that 2 1-1 trains will have a combined throughput of 120 stacks/min using the same length of tracks as the 1-3 configuration.
Answer the following questions correctly (values are fictional):
A 2-6 train travels 1 km in 2 minutes to move 240 stacks of items.
A 2-2 train travels 1 km in 1 minute to move 80 stacks of items.
- What is the operation of both trains?
Pull - Which train has the lowest throughput?
2-2 - Which train has the most rolling stock?
2-6 - What is the throughput per front locomotive (stacks/min) of each train?
60 and 40 - What is the throughput per rolling stock (stacks/min) of each train?
15 and 20 - Which train is the most fuel efficient?
2-6 - Which train is the least throughput dense?
2-6
PART 2: SO I DID THE MATH...
For consistency's sake, I'll be exclusively using pull trains in this part, but the principles discussed are the same for top and tail trains.
Size matters
I began my examination by simulating a locomotive pulling 1 to 12 wagons.
Throughput of coal powered trains in a pull operation traveling for 2 km
| Configuration | Throughput per front locomotive achieved (stack/min) | Throughput per rolling stock achieved (stack/min) |
| 1-1 | 69.7 | 34.8 |
| 1-2 | 125.6 | 41.9 |
| 1-3 | 170.9 | 42.7 |
| 1-4 | 207.5 | 41.5 |
| 1-5 | 236.8 | 39.5 |
| 1-6 | 259.6 | 37.1 |
| 1-7 | 276.7 | 34.6 |
| 1-8 | 288.4 | 32.0 |
| 1-9 | 294.9 | 29.5 |
| 1-10 | 296.5 | 27.0 |
| 1-11 | 292.9 | 24.4 |
| 1-12 | 284.2 | 21.9 |
I found out that something as simple as using a 1-2 configuration instead of 2 1-1 trains nearly doubles fuel efficiency; which continues to rise until the 11 wagons mark, where it finally starts diminishing. However, throughput density peaks very quickly, maxing out at 42.7 for a 1-3 configuration, and plummeting to half that for the last train.
The takeaway is that fuel efficient configurations will tend to have a higher proportion of wagons than throughput dense ones.
2 heads are better than 1
Next, I simulated a range of front locomotives pulling 1 to 100 wagons to find out the optimal configurations for each number of locomotives.
Throughput of coal powered trains in a pull operation traveling for 2 km (maximizing for fuel efficiency)
| Front locomotive count | Highest throughput per front locomotive achieved (stack/min) | Optimal configuration | Improvement in throughput over the previous configuration (%) |
| 1 | 296.5 | 1-10 | NA |
| 2 | 366.5 | 2-20 | 23.6 |
| 3 | 391.1 | 3-30 | 6.7 |
| 4 | 403.6 | 4-40 | 3.2 |
Each front locomotive added increases the fuel efficiency of the optimal configuration, but with smaller and smaller returns per locomotive added.
Throughput of coal powered trains in a pull operation traveling for 2 km (maximizing for throughput density)
| Front locomotive count | Highest throughput per rolling stock achieved (stack/min) | Optimal configuration | Improvement in throughput over the previous configuration (%) |
| 1 | 42.7 | 1-3 | NA |
| 2 | 50.6 | 2-7 | 18.5 |
| 3 | 51.9 | 3-11 | 2.7 |
| 4 | 52.4 | 4-15 | 1.0 |
In accordance to my previous observation, throughput dense configurations have significantly lower ratios of wagons to locomotives than fuel efficient ones. There's also the same decreasing gains in the maximized criterion per locomotive added.
To sum up, adding front locomotives improves both fuel efficiency and throughput density, but with shrinking increments at each turn. Furthermore, adding a front locomotive increases the optimal proportion of wagons in a pleasantly linear fashion.
Fueling ludicrousness
So far, I've only concerned myself with locomotives powered by coal; so what happens when better fuels are used?
Throughput of solid fuel powered trains in a pull operation traveling for 2 km (maximizing for fuel efficiency)
| Front locomotive count | Highest throughput per front locomotive achieved (stack/min) | Optimal configuration | Improvement in throughput over the previous configuration (%) |
| 1 | 391.0 | 1-12 | NA |
| 2 | 464.9 | 2-24 | 18.9 |
| 3 | 490.4 | 3-36 | 5.5 |
| 4 | 503.2 | 4-48 | 2.6 |
Throughput of rocket fuel powered trains in a pull operation traveling for 2 km (maximizing for fuel efficiency)
| Front locomotive count | Highest throughput per front locomotive achieved (stack/min) | Optimal configuration | Improvement in throughput over the previous configuration (%) |
| 1 | 684.6 | 1-18 | NA |
| 2 | 764.2 | 2-37 | 11.6 |
| 3 | 791.2 | 3-54 | 3.5 |
| 4 | 804.7 | 4-72 | 1.7 |
Throughput of nuclear fuel powered trains in a pull operation traveling for 2 km (maximizing for fuel efficiency)
| Front locomotive count | Highest throughput per front locomotive achieved (stack/min) | Optimal configuration | Improvement in throughput over the previous configuration (%) |
| 1 | 1034.2 | 1-25 | NA |
| 2 | 1117.1 | 2-51 | 8.0 |
| 3 | 1145.0 | 3-76 | 2.5 |
| 4 | 1158.7 | 4-100\) | 1.2 |
\ Trains with more than 100 wagons aren't simulated, and so the most efficient configuration might use a greater number of wagons; however, the difference would be negligible due to the linear scaling of configurations.)
When maximizing for fuel efficiency, the already large proportion of wagons of optimal configurations becomes absurdly gigantic; growing by 20 % for solid fuel, 80 % for rocket fuel, and a wacky 150 % for nuclear fuel.
Throughput of solid fuel powered trains in a pull operation traveling for 2 km (maximizing for throughput density)
| Front locomotive count | Highest throughput per rolling stock achieved (stack/min) | Optimal configuration | Improvement in throughput over the previous configuration (%) |
| 1 | 50.4 | 1-3 | NA |
| 2 | 55.5 | 2-8 | 10.1 |
| 3 | 56.6 | 3-12 | 2.0 |
| 4 | 57.0 | 4-16 | 0.7 |
Throughput of rocket fuel powered trains in a pull operation traveling for 2 km (maximizing for throughput density)
| Front locomotive count | Highest throughput per rolling stock achieved (stack/min) | Optimal configuration | Improvement in throughput over the previous configuration (%) |
| 1 | 63.6 | 1-4 | NA |
| 2 | 66.1 | 2-10 | 3.9 |
| 3 | 66.7 | 3-15 | 1.0 |
| 4 | 67.0 | 4-19 | 0.4 |
Throughput of nuclear fuel powered trains in a pull operation traveling for 2 km (maximizing for throughput density)
| Front locomotive count | Highest throughput per rolling stock achieved (stack/min) | Optimal configuration | Improvement in throughput over the previous configuration (%) |
| 1 | 70.1 | 1-6 | NA |
| 2 | 71.4 | 2-12 | 1.9 |
| 3 | 71.8 | 3-18 | 0.6 |
| 4 | 71.9 | 4-24 | 0.1 |
While the proportion of wagons also increases for throughput density, it does so more reasonably: about 5 % for solid fuel, 35 % for rocket fuel and 70 % for nuclear fuel.
Across the board, there's an increase in the proportion of wagons the higher the grade of the fuel is.
The whole 9000 yards
Something that should be obvious is that distance affects throughput; the more ground a train has to cover, the less its throughput will be. But does distance also affect what the optimal configuration would be in a significant way? To know, I took the optimal configuration for a given number of locomotives, powered by a given fuel, for a given distance; and compared it to 2 other neighboring configurations.
https://i.redd.it/o02zjb1iwrt31.png
This first graphic shows us throughput per front locomotive of 3 configurations relative to the highest achievable throughput per front locomotive, depending on distance. All of them have a single coal powered locomotive. Distance does not seem to affect which configuration is optimal.
https://i.redd.it/hfcs3k4lwrt31.png
In the second graphic, the number of front locomotives has been bumped to 4. While we do see a change in optimal configurations depending on distance, it doesn't happen until 5 km, and the benefit never exceeds 5 %.
https://i.redd.it/axfddhsnwrt31.png
Here, the number of locomotives has been reversed back to 1, but they are now powered with nuclear fuel. Just like before, there is no substantial difference in optimal configuration.
https://i.redd.it/9eeqb3sqwrt31.png
For throughput per rolling stock, the story is very different; the optimal configuration at 250 m becomes the worst performing at 2 km; while the 1-9 configuration starts at below 80 % relative throughput to becoming the best configuration after 4 km.
https://i.redd.it/a85vbdzrwrt31.png
Increasing the number of front locomotives to 4 gives similar results, with the best performing configuration at 250 m becoming the worst as distance grows, and vice versa.
In a nutshell, the most fuel efficient configuration for a given fuel and number of front locomotives stays effectively the same no matter the distance; contrary to throughput dense configurations, who's relative throughput is greatly affected, especially for short distances.
PART 3: ANSWERING THE QUESTION
Finally.
Choosing which criterion to maximize
Before choosing a configuration, you must settle on what to maximize; either fuel efficiency or throughput density. I've thought of some comparable aspects to help you make that decision.
Pros (+) and cons (-) of fuel efficient and throughput dense configurations
| Aspect | + or - | Fuel efficient configuration | + or - | Throughput dense configuration |
| Maximized criterion | NA | Highest throughput per locomotive. | NA | Highest throughput per rolling stock. |
| Number of trains | + and - | Smaller, with longer trains; easier to manage but less flexible. | + and - | Greater, with smaller trains; harder to manage but more flexible. |
| Optimal configuration | + | Is almost constant, no matter the distance to travel. | - | Varies depending on distance, especially for short routes. |
| Infrastructure | -- | Your loading station and intersection blueprints must be adapted to accommodate the very large footprint of a train configuration you've likely never used before. | ++ | The smaller size of configurations makes all railway infrastructure relatively easier to visualize and plan out. |
| Nuclear fuel | + | Using the highest grade of fuel is more practical due to having less locomotives to refuel overall. | - | Consumes relatively more fuel; you might not be able to power all your locomotives if you lack uranium. |
| Safety | + | Less trains means you're less likely to be ran over. | - | More trains means you're more likely to be ran over. |
| Performance | ++ | Less trains means more UPS. | -- | More trains means less UPS. |
Choosing a configuration
Once you've chosen your criterion, the next step is to decide how many front locomotives you want.
I've done much of the lifting here and compiled recommendations based on an average of optimal configurations for both 1 and 2 frontal locomotives, powered by every grade of fuel, for both pull and top and tail operations.
Recommended fuel efficient configurations (250 m to 8 km)
| Preferred fuel | Recommended configuration (pull operation) | Recommended configuration (top and tail operation) |
| Coal | 1-10 or 2-19 | 1-9-1 or 2-19-2 |
| Solid fuel | 1-12 or 2-25 | 1-11-1 or 2-23-2 |
| Rocket fuel | 1-18 or 2-37 | 1-17-1 or 2-37-2 |
| Nuclear fuel | 1-26 or 2-53 | 1-25-1 or 2-51-2 |
Recommended throughput dense configurations (250 m to 1.5 km)
| Preferred fuel | Recommended configuration (pull operation) | Recommended configuration (top and tail operation) |
| Coal | 1-2 or 2-5 | 1-3-1 or 2-7-2 |
| Solid fuel | 1-2 or 2-5 | 1-3-1 or 2-7-2 |
| Rocket fuel | 1-2 or 2-7 | 1-3-1 or 2-9-2 |
| Nuclear fuel | 1-4 or 2-7 | 1-5-1 or 2-11-2 |
Recommended throughput dense configurations (2 to 8 km)
| Preferred fuel | Recommended configuration (pull operation) | Recommended configuration (top and tail operation) |
| Coal | 1-4 or 2-9 | 1-5-1 or 2-11-2 |
| Solid fuel | 1-4 or 2-9 | 1-5-1 or 2-11-2 |
| Rocket fuel | 1-6 or 2-13 | 1-7-1 or 2-15-2 |
| Nuclear fuel | 1-8 or 2-17 | 1-9-1 or 2-21-2 |
Note that some configurations might have had a wagon added or substituted for the number of rolling stock to be odd; see this post.
As configurations neighboring the optimal might have very similar values to it, you might want to cut down on complexity and use shorter configurations then those recommended, in which case I heavily encourage you to download the workbook (link at the bottom of this post).
PART 4: CONGRATULATIONS, YOU MADE IT
I used to think 1 was prime
This was a rather involved post, but I wanted to explain in detail my reasoning for choosing the aforementioned recommended configurations; that way, if mistakes were made, someone more knowledgeable could easily point to the issue. If you notice a typo or miscalculation, or if I tackled something from the basis of a flawed premise, be sure to tell me in the comments; I'll try to keep this post updated to reflect all of your pertinent feedback.
Also, English isn't my first language: I made efforts to be as clear and concise as possible, but if you see something that you could explain better than I did, let me know.
Thank you for reading!
Answering feedback
- Why use fuel efficient (longer) trains?
If you want to achieve a given throughput with the fewest trains possible. - Why use throughput dense (shorter) trains?
If you want to achieve a given throughput with the smallest railway network possible. - I don't think my ore patches are big enough to justify using longer trains.
The output of your ore patches is irrelevant with buffer chests. Simply have the same train load at multiple outposts once they're full. - Won't longer trains break my intersections?
If you want to use longer trains, you will need to plan all your railway infrastructure in accordance. Keep in mind that using longer trains also means you'll have less trains competing for intersections. - Silly OP, do you know how comically large a loading station for a 2-53 train is?
Yes.
Links and acknowledgements
![[link]](https://i.redd.it/uw8jooqk8ut31.jpg){kind=link}
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![[link]](https://i.redd.it/inxeksa8itt31.jpg){kind=link}
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