Okay, so it’s going to get complicated.
Splines for the roads seems like the right idea but then again I’m not sure. The decals idea with a sequence node seems like the best plan. So you’ll need to have variables for each bit of road, and then use a timeline and a sequence node to path things out.
However, I am thinking I’m completely wrong with how materials can be manipulated, which means the timeline/sequence combo would be for a spline. Materials (the decals) would be modified on their material graph. I couldn’t find a way to manipulate the decals as intended from an event graph.
I would suggest looking into a few fade tutorials, feel free to take your pick as there are many and they’re mostly identical. I think this is a situation where amassing knowledge will unlock the path forward. HOWEVER there is one thing I know we’ll have to figure out, and that’s getting the decal to fade from point A to point B, then immediately starting the next decal/s from point A to point B, and so on, and so on. I’m thinking local coordinates on the decals themselves will be used instead of just flat “X” and “Y”. It’s going to take some doing, this is a pretty advanced thing. I could help you fade them in and out, but doing like you say I’m unable to provide direct help, only direction 