A Swing Bridge instead of a Duck Under

[ngauger]

ok - now we have the frame completed, time to attach it & run

Attach a 2X4 to the side of the layout as shown below. Screw the hinges to the 2 X 4.
   
If you have a leg you can build on, like I did - build onto it.

I just used a second 2 x 4 as shown then attached the vertical "bridge" 2 X 4 to that - ending up with 4 2 X 4's counting the layout's leg. Notice I Had to make a cut out on the 1/4" plywood for the top hinge.