How would they be able to quickly take the wheel and brake if something happens? I think the opposite is true, if you need longer reaction time it's probably a bad idea to not be fully immersed in the driving until an accident is imminent.

I'm thinking of a scenario where the driver is holding the wheel, but the computer is actually doing the driving most of the time while giving just enough feedback to the driver to feel like she is in charge.

In our tests a decade ago, we found that shared autonomy was actually much more frustrating for users than either full or no autonomy. When you were telling the computer to go over there and the computer wanted to go over here, it left all of the users frustrated and complaining that the computer wouldn't let them go where they wanted. Maybe you can come up with a better adjudication system than we did, but it is very tricky to design the system so that it catches when the user does something stupid but not when they are doing the right thing- if the computer could figure out the right thing you wouldn't need the human!

Interesting, cool to hear your experience!

It's actually harder to drive in these scenarios because your reaction time needs to be faster and your takeover has to be more aggressive. Imagine an edge case where the car veers toward another car unexpectedly. This isn't guaranteed to be avoided by level 3.

The same elderly people who drive through the front of buildings because it takes them so long to recognize they hit the gas instead of brake?

I think this indicates where level 3 is a slippery concept: it looks like it could be useful in this case, if you think only of the times when it works properly, but the only reason for a system to be level 3 is that it cannot qualify for level 4, meaning explicitly that it cannot be considered safe enough without having an alert human to fall back on.

I took a look through the level descriptions for a level where the human is driving but is being monitored by the system, but they all seem to be versions of having the system drive while being monitored by a human. Maybe we can do more in the way of collision avoidance as the technology progresses towards true autonomy.

I think so, but only with substantial geofencing.

I think you need level 4 for them.