Who cares about the other runes, it's all about the teleportation runes.

elevate the bridges!

The main reason I like minecart travel around our world is because it would give us all a big project to work on.

We could beautify it, with elaborate bridges and tunnels running through mountains.

I was picturing just a crude railroad track and nothing else, thats why I wanted underground lol.

But like Jonus said, it's oh so very easy for the entire system to collapse. Random cow on the track? Bam, sending you back the way you came! Imagine all the carts that will be left on the track! All it takes is a single track missing(or redstone torch) to break it as well. So not only do you have to manage to finish the project, that's a lot of upkeep over a lot of area.

Railroad can be a restricted region, but that wont stop cows from getting brave and playing on the tracks

Sadly it can't. As far as I know protected regions are restricted to cuboids.

these problems are solved by simply elevating the tracks

as far as the other stuff like abandoned carts and the like, that would either have to be handled with a mod like Minecart Mania. Collision with other players parked at stops could technically be done via a switch that activates via rail pressure plate.

Kinda farfetched, but worth a test. guess i got a new mini project to try out.

Elevated tracks would work, but they'd need to look nice, a Roman aquaduct style look might look nice for it

You still have to deal with abandoned carts (players logging out or accidentally launching a cart off), players on the tracks (walking the rails, or having lost their cart for above reasons) and following behind a player who moves slower than you. And don't forget lighting, mobs spawn on tracks as well.

Your also forgetting how lightning can break the railroad tracks, and the thing is that with so many things far away from eachother it would be hard. Plus how are we supposed to stop at where we want to get off without accidentally abandoning the cart? It would be going fast, and people would let it just keep going. Unless we made it a complete circuit and had the carts spaced out evenly so they could keep going around empty for other playersto get in,

Personally if its above ground I think a water way aqueduct would be better, so people could use boats and the current.

It's not really a matter of if it's possible or not, it's a matter of is the time and effort to not only make it, but manage it, is worth it. I just don't think it is.

Boats are even worse off in SMP than carts. They can break at the slightest touch of... nothing, and you don't get the materials back to make another one.

there are always mods do fix the problems, but on a survival multiplayer server like ours, it might be too hard to maintain.

maybe on a creative server, with unlimited resources