Back in 1860 nobody had even conceived of an automobile or the telephone.
They had plenty of laws for cutting telegraph lines, which did exist at the time.
When the telephone and automobile were each widely deployed, laws were created to address the social affects brought on by these advances in technology such as negligent vehicle operation and wiretapping.
The fact that the laws Had to evolve was a result of society recognizing the utility these inventions brought to bear.
The law is not a static thing, it is constantly evolving to match the needs and whims of society.
Insurance companies, on the other hand will require standardized testing at some point for policies to be granted. I suspect that the car makers have been developing such standards with the insurance companies, as such the law will have to catch up.
My prediction is:
Ultimately, autonomous cars will be subject to two standards:
1) if the on board computer/data logger indicates there was user intervention, and
2) if there was no user intervention.