I found this article about importing terrain and terraforming on the BeamNG.drive wiki. How do I enable this in my editor? Will this be implemented in the future? https://documentation.beamng.com/beamng_tech/terrainandroadimporter/
That is Beamng.tech. A different product, which has a lot more features than BeamNG.drive. It's for commercial and research organisations, although I believe the tech often trickles down into BeamNG.drive I have a somewhat more involved process I use for smoothing roads for my maps, which outline here: https://www.beamng.com/threads/map-in-an-evening.91991/ Hope this helps.