The carts do not switch freely at junctions. You can prepare a multitile junction as described above, and there might be switches later as mentioned above. At stop tiles, where a dwarf sets it on its way, you get a full fourway ability to send it on its way. Runaway carts hitting a T-junction will not pick a side -- they will continue on in violence.
In the multitile junctions, it doesn't care so much about the direction, so a cart coming up the wrong way will just continue along down the track.
I haven't done links to stops, though that's a reasonable enough thing to do. The track can't be powered under the stops since we are still stuck with the one building per tile limit, and the powered rollers are a building (like axles and gears).
Well, that crushes a lot of
my hopes and dreams, at least unless/until we get powered stops that can automatically launch carts.
This basically means we need individual dwarves for every intersection to manage traffic, or else we can only build individual loops, with no complex traffic networks, and it ruins most cart logic operations.
What we
really need is an ability to have track switches, or else rollers under stops that launch a cart in a direction
that can be changed mechanically, based upon a lever, pressure plate, or rotation of a gear. Then, we can have some truly wondrous cart mechanics, where destinations are altered based upon cart/water/mechanism logic.
I'm using inverted double lines for rails. Those'll either be distinguished from the hidden engravings walls through a color convention, or hidden engraving walls will be altered entirely. I don't like single line rails.
And minus an init option, that's basically going to ruin walls for graphics pack users.