Glad you liked it! 
If I remember correctly, I had two cameras: one on depth -1 and one on depth 0. The 0 would render everything that would be “above” the tunnel, and the -1 would render the tunnel itself. That way, it’d appear as if the tunnel was above the rest, and most importantly, the ground. 
The way that works is simply by attributing Layers to the particle systems, then setting the culling mask accordingly on each camera.
As for the neon style, that’s a style I’m going for. I could remove all glows and post process, but… well I just kinda like it. 