Culling Example for the Racing Game

I've made up a graphic to demonstrate the principle of culling parts of the environment to help with performance in racing game levels. I thought I'd share with the rest of folks...maybe a visual will help clear up aspects of the idea.

 

Hello, Thanks this is really nice, and the best illustration ever seen.
But I have few questions, how can I divide the mesh of road and environment?
How can I divide the scene in View Areas? Is this view area, called in Unity 4, Occlusion Areas?
To have this, I have to develop this with script, or this is what Occlusion Culling does?
And a last question:
If I have an enemy which is driving in an occluded area, does it fall down, because the colliders are occluded?
Thanks