Here’s my solution (it’s the one in the book):
And here’s the link:
http://www.lodev.org/jstumble/?board=rrereree0ereerrelee0lreelrelererleelexeerelreerleli
Description: If you trace the left-most path, the only way a blue ball can get into the interceptor is if both of the bits are pointed right to start. Otherwise you end up with a red ball.
I forget exactly how I solved this one “live”, but there are some obvious optimisations for the above that can save several ramps without significantly changing the approach. You can replace the 5 ramps coming off the left of the lower bit with 3 ramps going down/right to join the path from the crossover to the interceptor, and you can also swap the crossover with the ramp up/left from it, rearranging the ramps leading from the red source to save another ramp - saving a total of 3 ramps by merging the two paths to the interceptor as early as possible.
Of course, the changes would leave the solution harder to “read” by eye since there wouldn’t be the separation between the various paths.