Not news to Google
I'm always supportive of new research, but I'm pretty sure that Google already knew this. From the great Oatmeal (http://theoatmeal.com/blog/google_self_driving_car):
"The car we rode in did not strike me as dangerous. It struck me as cautious. It drove slowly and deliberately, and I got the impression that it’s more likely to annoy other drivers than to harm them. Google can adjust the level of aggression in the software, and the self-driving prototypes currently tooling around Mountain View are throttled to act like nervous student drivers."
and also
"They're intended as moderate-distance couriers, not open-road warriors, so their max speed is 25 miles per hour."
It sounds like Google's done a ton of UAT, and they've found what this study confirms: that passengers in their cars want it to go slower and be more cautious than they themselves would. So that's what they do!
Biting the hand that feeds IT
