[gojomo]

A problem with trucks as the leading-edge is that they're already a bit alien to the public and policymakers: resented in traffic, feared out of proportion to actual risks, underappreciated as some narrow corporate/union interest. If they're the test case, enthusiasm will be lower, regulation more costly/cautious, and the public vaguely suspicious, primed to assume the worst when anything goes wrong.

[protomyth]

Plus, people drive like idiots around them. It is amazing what normally sane people will do in the presence of a truck.

[gojomo]

Yep. People who know they're around a self-driving car may act weird, too: gawking at or challenging the software. (The young and reckless might even play chicken with autocars for thrills.)