Is there a way to create AI trains on other tracks?

It seems AI trains can only be placed at the track 0. Does openBVE support AI trains on other tracks like BVE5 does?
Or else, can it be achived by using the TrackFollower function in Animated Objects? It seems doesn't support following other rails. I think a function like "TrackFollowerTarget" would be better.

Sorry, there isn't, and this isn't likely to change at the minute.

The issue is a complex one, but it's essentially related to the route design format.

openBVE (and by extension BVE2 / BVE4) only support a single true track- Rail 0.
Everything else is simply worked out as a relative position to Rail 0.
In order to support secondary tracks, as well as the positional vectors, we'd need information on the curve radii of said tracks as an absolute minimum, which the current routefile format simply doesn't provide

You can use TrackFollowerFunction as a fake but good looking solution, yes. I think this is what you mean: https://www.youtube.com/watch?v=jiwcEZ5mRIw

You can find the route with the TrackFollowerFunction trains in it here: http://www.bveklub.hu/kiralyliget