Usually to switch tracks, you use the .turn command. Turn takes a ratio (of something I cant quite recall). Typically I've seen stuff like .turn 0.16, If I remember correctly this will switch it one track length to the right. Negating it (.turn -0.16,) will switch it to the left.
So if you have 2 parallel tracks A and B (A is on the left and B is on the right) and they are smacked right next to each other (which should simply be 4m), and you are on track A, .turn 0.16 should switch you onto track B. Then you would use the .rail command to readjust/add the other tracks accordingly.
I'm pretty sure thats a vague answer, and somebody else can probably offer a better explanation, but see if that helps.
There is a entry on turn on the wiki, though I dont really like it very much since it explains little to nothing, but it may be good for reference.
http://wiki.bvestation.com/index.php?title=CSV_Routes (Scroll down to where it says Track.turn)