‘To him who looks upon the world rationally, the world in its turn presents a rational aspect.’ –Hegel
Google started testing their cars on public roads back in 2009, long before any regulations were even dreamed of. An examination of the California Vehicle Code indicated there was nothing in there prohibiting testing.
For testing purposes, Google has a trained safety driver sitting behind the wheel, ready to take it at any moment. Any attempt to take the wheel or use the pedals disables the automatic systems and the safety driver is in control. The safety drivers took special driving safety courses and were instructed to take control if they have any doubt about safe operation. For example, if a vehicle is not braking as expected when approaching a cross walk, take the controls immediately, do not wait to see if it will detect the pedestrians and stop.
The safety drivers are accompanied by a second person in the passenger seat. Known as the software operator, this person monitors diagnostic screens showing what the system is perceiving and planning, and tells the safety driver if something appeared to be going wrong. The software operator is also an extra set of eyes on the road from time to time.
Many other developers have taken this approach, and some of the regulations written have coded something similar to it into law.
This style of testing makes sense if you consider how we train teen-agers to drive. We allow them to get behind the wheel with almost no skill at all, and a driving instructor sits in the passenger seat. While not required, professional driving instructors tend to have their own brake pedal, and know how and when to grab the wheel if need be. They let the student learn and make minor mistakes, and correct the major ones.
The law doesn’t require that, of course. After taking a simple written test, a teen is allowed to drive with a learner’s permit as long as almost any licenced adult is in the car with them. While it varies from country to country, we let these young drivers get full solo licences after only a fairly simple written test and a short road test which covers only a tiny fraction of situations we will encounter on the road. They then get their paperwork and become the most dangerous drivers on the road.
In contrast, robocar testing procedures have been much more strict, with more oversight by highly trained supervisors. With regulations, there have been requirements for high insurance bonds and special permits to go even further. Both software systems and teens will make mistakes, but the reality is the teens are more dangerous.