Simple howto for Complex phys mesh in Blender

I’ve spent way too long without seeking help, basically I don’t know how to section hitbox’s and do that stuff and make it work, I’m making a big road and it needs to be true to it’s simple yet vast geometry.

I looked at this thread but got impatient trying to section the ‘peices’ if I even understood how to section them.
http://forum.facepunch.com/showthread.php?t=1316925

I’ve sectioned the model into 30 pieces for optimization purposes, so what would be a simple and recreatable way to get the physics mesh to represent the model accurately.

PS: I acidentally put this in the mapping section ;-;