The most energy-efficient means of transport by land is by railway/railroad, due to the minimum rolling friction of smooth steel wheels on smooth steel rails. The down-side is that this makes it impossible to stop a train quickly or steer it clear of obstructions, and thus the need for sophisticated signalling systems, and fences or other impedimenta to stop animals, vehicles, pedestrians and others from getting on to the tracks. When you consider how many trucks or buses (and their drivers) that would be needed just to replace one train journey, it can be seen that - short of inventing Star Trek-type teleportation - nothing is ever going to replace the railways.
Air travel is of course a lot faster over distances of around 600 miles or more, but less energy efficient, and only of use for small loads of passengers or freight.
As to automated trains, most of the London Underground system is already 'automatic', in the sense that the driver 'tells' the train when it is safe to drive itself to the next station, but only after he/she has checked that the train has stopped correctly, opened the doors to let the passengers on and off, closed the doors and again checked that it is safe to depart. The driver still has to remain in the cab depressing the 'Drivers Safety Device' (to indicate that he/she is still conscious/alive!), and ready to take over when the automatic equipment fails. The Dockland Light Railway system operated by London Underground takes it a step further in that - between stops - the train operator is free to roam the train, assisting passengers and checking tickets. This is because the trains are light-weight, relatively slow-moving, and quick to stop in emergency.
Automatic control of main line trains is much more problematic where stopping patterns differ from one train to another, as do their top speeds, acceleration rates, stopping distances, number of cars etc. etc.
Other than short end-to-end systems, such as airport shuttles, I do not think that the general travelling public would ever feel safe travelling on a deep-level 'tube' line or even a sub-surface subway train with out there being a trained member of staff on board. The same remark goes for long-distance main line trains thundering down the main lines at 100 mph and more.