The likelihood of the Teamster's union allowing (i.e., not obstructing) driverless cargo hauling to succeed in the US would be close to zero.
They might even end up with similar pay for less total hours away from home.
=> we need need fewer trucks
=> we need fewer drivers minding those fewer trucks
I fail to see what would make truck owners offer 'competitive salaries' given that there will likely be X>1 truck drivers competing for each 'truck minder' job, and that the job requires fewer qualifications (drivers do the minding today, and future minders will not need a drover's license)