Factorio Forums

I’ve been getting into trains recently and am constantly seeing mentions of left turns being the devil in the megabase. Why? What’s so bad about left turns? And if there is a problem how can I fix it?

Proper signaling is the key to efficient train routing. Many players (especially new ones) struggle with train signals and create deadlocks.
This can be especially problematic for longer trains as their sheer size is difficult to account for when crossing tracks.
The best thing you can do is learn how to signal your tracks properly.

MassiveDynamic wrote: ↑Sun Oct 25, 2020 3:37 pm Proper signaling is the key to efficient train routing. Many players (especially new ones) struggle with train signals and create deadlocks.
This can be especially problematic for longer trains as their sheer size is difficult to account for when crossing tracks.
The best thing you can do is learn how to signal your tracks properly.

I’m pretty sure I got my signaling down pat. I’ve been using a t intersection that I made myself and it’s working fine for the 5 trains in my base. I’m wondering what’s so bad about left turns In Specific?

MassiveDynamic wrote: ↑Sun Oct 25, 2020 3:37 pm This can be especially problematic for longer trains as their sheer size is difficult to account for when crossing tracks.

It’s the crossing that creates the issue.

Of course this assumes right hand drive.

Gamatron332 wrote: ↑Sun Oct 25, 2020 3:00 pm I’ve been getting into trains recently and am constantly seeing mentions of left turns being the devil in the megabase. Why?

As far as I know it's nothing more than the fact that with a right hand drive network (which is most common), left turns require crossing the path of trains going the opposite direction, which significantly impacts throughput.

With left hand drive, right turns have the same issue, of course.

Gamatron332 wrote: ↑Sun Oct 25, 2020 4:09 pm I’m pretty sure I got my signaling down pat. I’ve been using a t intersection that I made myself and it’s working fine for the 5 trains in my base.

5 trains make very low traffix, so any intersection will be fine.
What if you had 50 trains on the same route? There would be heavy traffic, and you would need to handle throughput issues. Intersections have limited maximum throughput regardless of proper signalling. And, some intersection designs are worse than others. "Good" intersections tends to be large and complex, and... most players just have no idea how to design high throughput intersections. The solutions are: organize things in some smart way to decrease traffic load, or avoid left turns.

SoShootMe wrote: ↑Sun Oct 25, 2020 4:25 pm As far as I know it's nothing more than the fact that with a right hand drive network (which is most common), left turns require crossing the path of trains going the opposite direction, which significantly impacts throughput.

With left hand drive, right turns have the same issue, of course.

i would say the same. On the most common right hand drive network ,if you take one train going from north to south and one train going the opposite from south to north. both can do a right turn at the same time without problems. But if they do a left turn, depending on your junction layout it can happen that they cross each other path, which would require one of them to stop to avoid crash. This stopping is what can create problems on busy network, since the train behind the one stopping could need to stop too. And the one behind it, and so on. Depending on how fast they accelerate back you can create traffic jam, or even deadlock if the traffic jam propagate up to another junction.

Maybe it's easier to explain saying one train goes straight from north to south. Another one going the opposite direction is fine turning right. But turning left would make their path intersect.

Ah thanks everyone! So I guess I need more of a stress tester trains setup... anyhow I’ll definitely be playing with this in mind more so that after I ignore and then wonder why my fuel train isn’t going as fast I’ll know the problem

In another thread you said that you only got as far as yellow science so far and only just built your first train. And I assume you hadn't launched a rocket yet. There is no need whatsoever for this much optimization in advance. There is never always more than one solution to issues. You can easily build megabases without caring about stuff like this. People build megabases with rail grids / city blocks and 1-4 trains (or even smaller trains). That's far from ideal, but it still works

Serenity wrote: ↑Mon Oct 26, 2020 1:07 pm There is no need whatsoever for this much optimization in advance. There is never more than one solution to issues. You can easily build megabases without caring about stuff like this. People build megabases with rail grids / city blocks and 1-4 trains (or even smaller trains). That's far from ideal, but it still works

Yes all true, except I think he meant "There is ALWAYS more than one solution to issues". I would add that there is no material cost for tearing down and rebuilding other than your time. On a few of my worlds. I've just used the deconstruction planner on the whole thing and started over. The only real need for perfect efficiency, JIT, or symmetrical design is for your own personal pleasure.

MassiveDynamic wrote: ↑Mon Oct 26, 2020 4:25 pm Yes all true, except I think he meant "There is ALWAYS more than one solution to issues".

Oops