Alternate Path Tracks

Ok, I've seen them in Hammer, I've seen them work in various games TF2 HL, etc but does anyone know how they actually work and how you code them?

I would like a cart to go down track 1, then the next cart to go down track 2 ant then the next cart that comes along down track 1.

Basically I want to make some randomness in something repedative.

Or the first 4 carts do the above and then the 5th takes a diferent route from the other.

How do I code it - I'm not getting the expected results - thanks.

Ok if I'm getting it right

cart moves node 1 to node 2 onpass (node 1) alt path to node 3 so the next cart that hits node 1 goes to node 3 and then at node 3 I can use the cart passing to reset node 1 to send the cart to node 2?

Am I understanding this right?

Perfect Just got it working right! I now have alternate paths working for my death carts so people won't get used to it always going down the same track.

Thanks so much!!