How can I make a wall around a road on a cars track? I'm new on blender and I'm doing (at least trying) a Assetto Corsa track.
The question is about creating a wall on the two sides of the road. 
I created a wall with a cube, added an array modifier pointing to my nurbs path and then I created a curve modifier, so the wall follows the middle of the road. But I can't edit the X axis of that wall, so I can't scale it to match the outside or the inside of the road. It looks like this:

Any suggestions?

Here I leave you my .blend so you can check anything you need. 



Thanks in advance for any help :)
Enter wall edit mode and move it along local Z axis, then duplicate it and move it again on the Z axis. To know better what you're doing, turn Display modifier in edit mode and adjust edit cage to modifier in modifiers stack.Like this: