You can import your own "bent" mesh as the ground, or wait for the next beta version for a new feature that will be a road that can be bent and curved from within BB3.
There's really only one choice, unless you have a lot of money, Blender. It is free and very capable....but the interface is quirky to say the least, and there's a steep learning curve, but follow one of the beginner's tutorials on YouTube and it will quickly get up to speed enough to make basic objects. There is a ton of support for Blender, and once you learn the interface it is a very capable product, far beyond anything you'll ever need in BB3.
