After swapping axis (because I forgot that OpenGL uses Y+ as up, I had to change the way I'm selecting where to place the road.

Now, I'm calculating the tangent at each point (the cyan lines). It gives a constant result that could be linkes to make a neat circuit.

@Ronflaix ooh, are these made of circular arcs, or…?

@notwa Yep, I'm using biarc interpolation for each segment.

@Ronflaix haven't heard of those before, glad i asked!