I think the real problem is more emotional. People are already scared of the big trucks. The majority of the population would be terrified driving alongside of driverless tractor trailers.
Most of the time you can’t even see the driver. And really, what do you want to be next to: a semi driven by somebody who hasn’t gotten enough sleep and just had a fight with his wife, or a robot? And really by the time they work it out for trucks self-driving cars will be in mass production, so we’ll have gotten used to the idea.