Circuit tile editor

I keep working on the circuit tile editor.

The idea is to make the circuit road with a bunch of connected tiles. I've finished all posible tile transforms/deformations to make the circuit turn left/right, going up/down, making the road wider/narrower, etc.

To be able to make a full circuit (excluding decorations like mountains, trees, etc, I need to: 

• Autogenerate a new tile from the last one, making sure than their vertices are connected.
• Connect the last tile with the first one.

EDIT

Thanks to the software renderer, I can show transparent back faces without pain: