By creating regulations that apply to the creation of those things? Level 1 AVs exist and as such regulations exist for AVs. These regulations apply to level 4 AVs despite being mostly theoretical.
The other commenter in this thread basically already answered this as well by talking about how manufacturers need to prove the safety of it before it can be green it.
How can something that does not exist be illegal?
By creating regulations that apply to the creation of those things? Level 1 AVs exist and as such regulations exist for AVs. These regulations apply to level 4 AVs despite being mostly theoretical.
The other commenter in this thread basically already answered this as well by talking about how manufacturers need to prove the safety of it before it can be green it.