What is this "problem"?Hello fellow Nauvians,
My request is a very simple one. It's a feature this game has been missing for far too long, and it has some pretty big implications for people who use double-headed trains, and even general QoL.
In the game's current state, trains that are on a multiple locomotive configuration will behave differently depending on which direction(s) the locomotives are facing. I will diagrammatically illustrate my point by showing a few examples of this.
> - Forward-facing locomotive
< - Rear-facing locomotive
= - Cargo/fluid wagon
Trains in a configuration where all locomotives contribute power:
==>, ====>>, >====>, ==>==>, etc.
Trains in a configuration where only forward-facing locomotives contribute power:
<====>, ====<>, etc.
The main takeaway from this is that if a train is moving from left to right in these examples, the locomotives facing to the left are just dead weight.
How can we fix this?Simple: make the locomotive facing the opposite direction of how the train is moving also burn fuel and contribute power to the train.
Why should we even do this?Locomotives actually weigh a lot and cost fuel efficiency and speed because the locomotive facing in the direction the train is moving has to do all the work. In a system that's primarily 1-4-1, the locomotive in the rear will not do anything until the train stops somewhere and then switches directions. This behavior means that there is a tradeoff between sacrificing compact track layouts (i.e. no loops, two-way tracks in stations) for acceleration and fuel efficiency.
In real life (at least in the US, I can't speak for other countries), it is very common to see freight trains that are dozens of wagons long that have multiple locomotives in the front and sometimes one or two in the rear. Unlike in Factorio, the direction the locomotives face are irrelevant to the power contributed. All of the locomotives are synchronized and controlled simultaneously by the driver. This means for instance you can have a train which is 100 cars long with a configuration like this, where all of the locomotives contribute:
Where I'm from, this config is pretty common on big freight trains IRL. Factorio really needs this in my humble opinion, because it will allow the player to have twice as many options when designing their train conventions, and incentivize the space efficiency gained with double-headed trains.
Potential design challengesThis is more on part of the player's design rather than any challenge with implementation. Since I'm not a developer I can't speak to how difficult this would be to implement, but because it's not some abstract or ambitious idea I would imagine it's pretty simple (unless it breaks something.)
In single-headed trains, how does the player prevent them from moving in the wrong direction, or arriving at the station facing the wrong way? Well, you could design around this by making your train configurations symmetrical or getting clever with signal placement or loops to prevent trains from turning around.
What about the aerodynamics coefficient? Yeah, if you didn't know about this, locomotives have a bonus to aerodynamics which reduces acceleration time if they're facing the same direction they're moving in and are towards the front of the train. This is pretty easy to pull off if you have single-headed trains, just have all of your engines in the front.
ConclusionI really think that this simple change to train behavior is a no-nonsense solution to an otherwise significant problem with running double-headed train conventions. As someone who always prefers double-headed trains, but always thought their behavior seemed a bit incompetent, I've really been wanting to see this and I've simply put off writing up a suggestion for it until now. With the new train stop feature implemented post-release in 1.1, it makes sense to me that our great Wube overlords might not ignore this post.
Anyway if you got this far, thanks for coming to my TED talk. Let me know what you guys think of this idea!