To change the height of roads, You need to install Move It ( it requires Prop snapping)
https://steamcommunity.com/sharedfiles/filedetails/?id=1619685021
https://steamcommunity.com/sharedfiles/filedetails/?id=787611845
Enable them on Content Manager.
Continue or Resume Game
Press M to activate Move It
Select the node (not entire road ) of the road you want to raise or lower.
Press Pageup / Pagedown ( fn + ↑ / ↓ )