From the end of the decreasing radius left turn at the top of the drawing, right where you sketched in the route, you could put in a a constant radius sweeper, with a little kick into the exit points. It would be just shy of 6 feet long, and would come almost over to the lanes traveling in the opposite direction, so a clear plexiglass catch wall might be needed. On my track, I have thought about a wall to separate, but it never seems like its needed.
Here's what I mean: