[awhitby]

That might be true for the simple case of following within a lane, although you only have to drive around to realize most drivers do not leave adequate following distance at all times to make this a pure physics problem. And neither is a good driver watching only the car in front, but also the brake lights of the cars in front of that, to help anticipate the car in front's likely actions.

But take an even slightly more complex example: you're on a two lane roadway and the car in the other lane changes into your lane, leaving inadequate stopping distance for you. You brake as hard as you safely can (maybe you have a too-close follower, too), but still there will be a few seconds when you could not, in fact, avert a collision if for some reason the car in front braked.

I have no idea what the legal situation would be: is it their fault if the crash happens within 3 seconds but yours if it happens after you've had time but failed to restablish your needed stopping distance?

Honestly even in the simple one lane case, I doubt you can slam your brakes on the interstate for no reason then expect to avoid any liability for the crash, blaming your follower for following too close.

Driving has a bunch of rules, then an awful lot of common sense and social interaction on top of them to make things actually work.

[Out_of_Characte]

A car changing lanes does indeed remove stopping distance. But thats also something human drivers are naturally more capable of understanding than waymo. It shouldn't have mattered where a vehicle is on the road. Any human is able to predict if a weirdly loaded vehicle making a turn has a chance of invading their lane and/or stopping distance. Its a complex problem for sure but that also shows that you need absolute proof that the software is able to generalise the problem. Especially if you want self driving cars to respect flow of traffic over stopping distance.

Even if your software is as good as it can be, I doubt you'll be able to get them to recognise how to resolve deadlocks. Which would also involve severe hindrance to emergency vehicles.