I would implore you to look to aerospace/DoD simulation technology, informed and validated by the real world, and systems engineering to replace 99.9% of the public shadow and safety driving you use. That practice is untenable, harms people for no reason and will harm far too many when you get to complex and actual accident scenario work.
It is impossible to drive the one trillion miles or spend over $300B to stumble and restumble on all the scenarios necessary to complete the effort. Many of which are accident scenarios no one will want you to run once let alone thousands of times. Also handover cannot be made safe for most complex scenarios, by any monitoring and notification system, because they cannot provide the time to regain proper situational awareness and do the right thing the right way.
SAE Autonomous Vehicle Engineering Magazine — End Public Shadow/Safety Driving
Common Misconceptions about Aerospace/DoD/FAA Simulation for Autonomous Vehicles
The Hype of Geofencing for Autonomous Vehicles
