Using Portals for AI
Although RSC discourages the practice, having a train emerge from a portal is a fairly simple process -- provided that the portal is correctly placed. The steps are these:
1) Place an AI engine or train near the portal ... facing away from it, of course.
2) Set up the AI engine or train's route and make sure that it runs correctly without interfering with other trains. I typically leave the last step until the entire scenario is complete.
3) Double click the portal: a fly-out opens at the upper right of the screen and can be pinned in place like any other fly-out. This one contains two buttons, labeled "add" and "remove", and a list box, as well as the name of the scenario and the name of the portal. To place the train into the portal, simply click the "add" button and then click any part of the train. The train's name then appears at within the list box. Click anywhere outside the fly-out.
This becomes trickier when two or more trains are to be hidden within the same portal. I don't much care for the term "spawn" being applied to what happens in during the scenario, because it suggests that the portal simply spits out one or more trains on its own, when the truth of the matter is that a good deal of planning has gone in to the process. One last note: to remove a train from a portal, double-click the portal to open its fly-out, click the "remove" button, and click the train's name. Careful! The train is now attached to the mouse pointer and if not placed correctly on a track it will simply vanish.
by Tom Pallen (oldprof)