You've essentially described the trucking industry, without the need to figure out linking or being limited to rail routes. Without the train length, you lose

You've essentially described the trucking industry, without the need to figure out linking or being limited to rail routes. Without the train length, you lose the efficiency. The sum of added traction drivers and energy storage on each car exceeds any savings you might gain by autonomous operations or possibly getting rid of the traditional locomotives. Convoy based self-driving tech on interstates is roughly mature enough as-is to operate as a drafting, self assembled train, if there was a desire/demand to implement it. But that goes back to political/social/business reasons.