Creating Very long transportation road in Unreal Engine

Hello. Using Cesium for unreal plugin and Google photorealistic 3D Tiles, I go to a specific location in world and there, I want to create a very long transportation road and a river beside that road. The roads length is about 105 kilometers, it is not straight and have some curves and the ground in project site is not totally flat and there is some low and highs. Knowing these information about project, what is the best solution for me? I personally use splines in landscape mode, but creating such a long and uneven road with splines is very time-consuming and exhausting. Is there any better solution or ang special plugin for this purpose? and another question. When I add road with splines to Google photorealistic 3D Tiles in Unreal engine, despite of saving my changes to project, when I reopen my project in Unreal Engine, my road doesn’t exists anymore. what’s the problem? How can I save the changes?

I don’t know about cesium or any of that “real” tiles stuff, bur a spline is just a set of points.

You can make an excel sheet with all the points, and import the spline.

This is normally done for stuff. Since for instance i have 3000 rivers/brooks and 7 major roads with around 1000 little ways to import in a 144km^2 gameplay area.

All you have to do is figure out a format, get a data source, and create a bluetility that will process that source and generate your spline for you.

Some times you can select the whole spline points and hit home to make them find the ground.
Wouldnt reccomend doing that on splines exceeding 100 points though.

And import wise, you want to avoid long loops or the engine times then out.
Build it so you plot 10 points at a time, then do something else (like add a random editor only mesh? Im using mile markers.) and plot more.