TL;DR
The lovely neon-colored lines show how the rail network splits into different sections, but also the directionality of each section.The direction is indicated by a small arrow. If the section goes in both directions, a little box/diamond is rendered instead. At a small scale, the arrows and boxes reduce to little blobs and look pretty much the same.
I don't know about you, but I feel like I have to squint here to tell whether a section goes into one direction, or two.
What?
I suggest making the arrows 3x bigger. I don't see why not -- there's enough space.Like I mentioned, the diamond-shaped indicator on a two-way rail can be mistaken for an arrow. I would remove it entirely, and simplify this into just lines and arrows. If there is a direction, it is indicated with an arrow, and if there is no direction, then there's just a line. This way, the difference between a one-way track and a two-way track should be very obvious, visually.
Note: I removed the arrow from the pink section going up, but I realize this is actually a bad idea. So this mockup is overly simplified. But what this shows well is that the arrows could be a lot bigger, and that removing the diamonds might be a good way to make one-way and two-way tracks much easier to tell apart, even from a distance.
Why?
My vision is getting worse at 32 I guess... I want to keep playing Factorio into my retirement years, so readability is important.Once you figure out how to do trains properly, you probably don't even need the game to visualize the direction for you. But I'm a noob with trains, and I built a big system that runs into issues all the time

