Agree on the BM&LP (and a couple of other mine RRs) as early automation. For that matter, BART originally was supposed to be fully automated, and for practical purposes is with the train attendants (drivers) not actually doing the "driving" absent emergency conditions. Don't forget the SkyTrain system in Vancouver, which was and still is completely driverless. Those are all closed systems, though. In the more open systems of the standard US RRs, even though steering isn't an issue, automation is more difficult due to the variety of environments and hazards that have to be handled. Also, the relatively light traffic on most US lines (other than some heavily-used main lines) makes it difficult to justify the private capital spending needed to support full automation.

Road vehicle automation is heavily supported by public and institutional research funding and policies. Relatively little funding is available for railroad research, and the regulatory system makes it difficult to do anything really new or disruptive. Also, automating trains just isn't interesting to the New Economy startups. OTOH, highway vehicle automation provides many interesting problems for AI & computer researchers, and techies in general, to work on.

Frankly, it's starting to look like the 50s-60s again, when freeways sprang up all over with public funding, kick-starting the long-haul trucking business and putting the kibosh on a lot of RR business. Expectations regarding shipping time and reliability changed to where RRs couldn't compete well for higher-valued stuff, and with vehicle automation improvements it looks like another increment of that is coming. US RRs won't go away - some things just can't practically be shipped by road, and a lot of stuff isn't actually as time-sensitive as some people think it is - but I'm afraid that they will become even more niche players for at least the mid-term (a couple of decades). RRs that survive through that might find a better competitive environment as fuel prices rise again and climate change issues become unavoidable.