After reading that report, it is unclear to me how the officer persuaded the car to pull over. I thought that Google car model didn't have a steering wheel, so even though I assume it had an occupant, they can't really "drive" the vehicle (when Google released e first video of that car it showed people being driven around in a parking lot by the car, which had no steering wheel). But that must not be the case, the version that is driving on public roads in the Mountain View area right now must have manual controls so that the occupant can take over if necessary.