The most likely thing (imo) that will happen will be highway trains...there will be a real human driver in the front of the caravan, maybe just in a van or car, and then 1-10 self driving heavy duty trucks behind them. They'll draft off of each other and do 99% of the long haul route in an automated way. Once each truck is near it's destination, it will peel off of the pack and park itself near the highway, at which…
It already happens according to legislation. Though, these vehicle are generally limited to 2 trailers, restricted to some loads), if road condition allows it.