A demand from the California DMV of eight companies testing self-driving cars has highlighted a number of areas where the technology falls short of being safe to operate with no human backup.

Self-driving cars with no human backup behind the wheel will be legal on California roads for testing and transporting the public starting April 2.

General Motors is in a race to be the first company to mass produce self-driving cars, but a recent crash with a San Francisco motorcyclist has illustrated the tricky challenge of assigning blame when an autonomous vehicle gets in an accident.

Amazon received a patent outlining a possible plan for “directed fragmentation for unmanned airborne vehicles” used in deliveries.