Running 2 trains at once

well...in that case I would say to use a transformer that has overload shutdown feature built into it.
MRC Tech series controllers come to mind but there may be other names that I don't know of too.
or for the best I would say to gap the connecting siding into its own 'third' block and hotwire up a doublepole switch to it to both track circuits.
the way that could work is say we have two oval and one long crossover track that connects both...throw the switch to #1 and a train from outside circle enters the crossover block...stop it there...flip the switch to #2 and the train is immedately on insidle circle power instead as it exists the block onto inside circle itself. --hope that made sense?
John Mycroft wrote:

The lego transformers have overload protection built in. If you just have two loops with points between them, you cant actually get them set up so they can short out.

Thanks DR & Dean
I like the idea of the double pole switch and it's nice to know about the built in overload protection. My concern about short circuits etc is that the trains will be run by my 6 year old son and it is not beond the realms of probability that, with 2 loops connected by a siding, he could have one controller wired up so that turning it counterclockwise means the train goes forward and have the other one connecte the other way round (should have called the kid "Murphy" :>} )
T'other option is to have the two loops cross each other with 2 cross tracks but not be connected at all. So long as we don't burn the house down...