Really nice ! I wonder what you are using to build the tracks, can you describe your workflow ? Thanks !
Sure, I'm using ProBuilder straight in Unity's editor for 'terrain' and 'props', it's a great tool for quick iteration. Actually, there isn't a lot of workflow there. I've cheated a little(?) - if you observe carefully, you'll notice, that there's only one turn with some slight variations that's tricky mirrored and aligned so that I can stack and angle them together (didn't do particularly good job on those geometry light leaks, though).