We're very close to that. Problems are:
1. The technology is mostly there but rarely all there. The US, for example, is rolling out PTC, which is 90% of the self-driving-train solution (though it's intended to be merely a safety upgrade), but PTC will not be universal. While Europe is way ahead of the Americas on this, largely because they're not stupid, boneheaded, and corrupt when it comes to transportation policy (and thus they take trains seriously rather than deliberately running them down, making them all but unobtainable, and then claiming nobody wants them when nobody rides once-a-day museum relics whose stations are 50 miles away from anywhere you want to go and whose speed rarely breaks 50mph) PTC is still not universal.
2. You do, still, need equivalents of the technologies going into, for example, Google's self driving car. Did a tree fall on the track? Has heat bent the rails out of shape? Is there an idiot driving parallel to the train who's likely to jump the tracks at the next crossing (well, in fairness, human engineers can't generally deal with that either, and usually have to suffer the trauma associated with slamming on the brakes, getting out, and finding bits of someone's head on the track.) What about a washout?
3. Yeah... unions. I hate blaming unions for anything, largely because 90% of the time when someone claims unions are the thing that killed a particular industry or stops needed reform from happening, they're making it up or at the very least massively exaggerating. In this case, however, the unions have this issue on their radar and have been fighting smaller crews, and expressed concerns that PTC = 1 engineer or eventually no engineers.
There are automated systems out there, but they generally run in completely enclosed subway tunnels and have a high degree of human monitoring. Until PTC can be augmented with techologies that can visually and non-visually verify the tracks ahead are safe, we can't really automate any major conventional intercity railways.
But I bet it wouldn't take a year for, say, a team made up of Google's self driving car engineers to create those technologies.