Well, here's my first dueling/racing coaster. It's a bit on the rough side but it's still ridable and realistic. It has several close calls with the ground, the supports, and the other train.
With this one, you have to let one train go around by itself, and when it comes back it should be pretty well synchronized with the other. If it's off by a bit (which it ususally is), take the train that is behind so that you will actually be able to see the other train during the fly-bys!
I think that's about it. Sorry if this one's a little rough, but I think it's still worth the download! Enjoy your ride!