hi.
i have a track for a 2d racing game.
i use 2D Toolkit for it.
you know , 2d toolkit have an option for collider , Polygon. so i add a polygon collider to my track, but it is only for one side!!? how can i have 2 side???
in below image you can see a green collider for inner circle ,
NOW the Question IS how can i have a suitable collider for outer circle ??
I guess that you’re checking and processing the actual on the vehicle (I guess you use one since I see a road)? If so, why not add a 2nd texture of your road, make the polygon for the outside of the road and tell 2D toolkit to use the INNER part as collider? Not sure that’ll work, but if it does it seems like the easiest way 
You’re not actually colliding with the road itself, but with anything except/outside the road. You might simply create two (or more) empty gameObjects with dummy textures for inner and outer sides of the road, add polygon colliders to them separately and disable texture renderer.