Mathlete:
I'll bet you 15-20 years from now there is a driver in the seat of all or nearly all semi's going down the road. The semi's may be robotic and autonomous, but a driver will be there as a fail safe. You may believe it's totally unnecessary, but I suspect they will be there. Planes have had autopilot for years, but there's still a whole bunch of people sitting in the cockpit. Drones are flying around in empty airspace, but somebody's still watching.
I by no means think that self-driving cars will be flawless. They're absolutely going to kill someone at some point, so your idea of humans as a fail safe is at least somewhat compelling.
Here is a thought experiment though.
By how many accidents per X miles does the combination of a human driver + robot driver need to beat the robot driver alone before the cost of having both in the cabin outweighs the savings on insurance premiums?
I don't know the answer to this question but I can bet you that the long-haul companies looking into automation are trying to figure that out though.
The BLS pegs the median semi driver's salary $39.5K a year. Add on top of that the cost of any benefits that this guy gets and the incentive to get him out of the driver's seat is already huge. As big of a factor as his salary is though, it's dwarfed by the opportunity cost of the 8 hours of downtime a day that the truck loses while it is waiting for it's human baby sitter to sleep, eat, and go to the bathroom.
FYI - Drones require a rated pilot in combat airspace. Have you seen the reg's the FAA has for US airspace? Semi's will be at least that restrictive.
If it is legislation, and not limitations on technology keeping people employed then my argument still stands. Whether they're "supervising" a machine that is better than they could ever be, or sitting at home collected a check because they're out of work, the net result is still human capital appearing as a negative item on most balance sheets.
If humans are so unnecessary in transportation, why do ocean freighters still have people on board? Think about it they are slow speed and do most of their travel in unpopulated areas. Seems like a perfect application, yet their is still a human fail safe on board.
Ocean Freighters aren't my area of expertise but I can say with confidence that they are no longer employing scores of dudes whose job it is to shovel coal into a furnace.
The mere fact that we're discussing timelines in terms of 15-20 years and not 150-200 years kind of shows where we're headed.
Human labor is losing ground on our machine and computer counterparts every day. I don't know if it will be 10 years or 50 years or whatever, but the day is coming. I think we should be ready for it and I think that getting ready for it involves at least pondering what a world would be like in which most people can't find jobs.