If you want to have two trains running at the same time you really need them on separate loops rather than sharing any track, here's an example: track1 by J Tassier, on Flickr
This uses Andy's "3 curves, 1 straight, 3 curves in the other direction" blocks three times so as to keep everything nicely in system, twice on the inside loop and once on the outside.
If you want something with a more irregular geometry then this is an example, I used blue rails for all of the straights to make it easier to see: track2 by J Tassier, on Flickr
This second track needed 42 straights though so not sure if you have quite enough.
