It is happening right now.
Rio Tinto are running 37 500 tonnes (41 325 US tons) trains over two hundred miles of main line hauled by three 4400HP GE locomotives controlled by the dispatcher two thousand miles away.
The line has a number of grade crossings, all equipped with barriers, light and bells and with video cameras monitoring the crossing. Of course, with that size of train, no on board crewman could stop clear of a crossing once it was in sight, even though all the trains have ECP brakes.
There is no need to have anyone other than the dispatcher to drive the train, since fixed blocks are used and the train "knows" its location and grade and the system is programmed with the optimum power and brake settings.
They started recording data for this system in 1975 and they haven't rushed anything. The remote control system was live in 2006 but the trains still had a single crewman at that time. I've seen photographs of UP power at Erie PA fitted with the same remote control system as Rio Tinto were using in 2006 (at about that time).
This is operated through a relatively low population area, but it is an area with a lot of tourist traffic on sealed highways.
Another major operator in the area had signs on their grade crossings forty years ago "Our trains take three minutes to cross this crossing, whether your car is on it or not".
They were trying to convey to outsiders that an iron ore train of 30 000 tons or more was not going to stop if there was an obstruction on the crossing.
I was riding such a train in 1978 (with two crew) when it made an emergency application due to a signalling error. Nothing derailed, but the train broke in five places (there were 220 cars) including a drawbar between two ore cars.
Another operator has indicated that they will go to crewless operation in the near future.
In Sydney, Australia's largest city, fully automatic commuter trains are currently operating. These have no grade crossings and all the passenger platforms have gates that open when the train doors open.
That is now...
In twenty years, locomotives with a crew will be the exception.
UP were testing it more than ten years ago...
Peter