Hi Rob,
the road will be not bumpy at all, unless you change the setting to have the road inherit more of the roughness of the main terrain.
By default, the road will "cut" a valley into your main terrain along the road path, and run through it mostly flat.
I chose this as the default approach, as otherwise it would have been next to impossible to make it work on any terrain. Now it's easy to use and it's really cool how many possibilities for new, interesting scenes come up once you have a procedural road at your disposal
Cheers,
Frank