Freeways are much, much less forgiving of abrupt speed changes and braking, which is something waymo (used to) have quite an issue with. Moving to freeways shows they are confident that won't be an ongoing issue.

Yes I was driving on a freeway last week and traffic went from 80mph to dead stop about as fast as I could stand on the brakes. I didn't hit the car in front of me with only a few feet to spare, and fortunately the driver behind me was also paying attention. The jam eventually cleared, and there was absolutely no indication of what caused it.

>> and there was absolutely no indication of what caused it

That's the Accordion Effect.

With enough cars on the road, one little tap of someone's brakes flashes their brake lights and it ripples upstream until the 80mph column of cars is forced to go to down to zero ASAP.

Emergency braking is much harder at freeway speeds.

At 35mph you can have something (radar/cameras) look a few meters ahead, then if there is a stationary obstacle you slam on the brakes.

At 60 that doesn’t work because braking distances are much longer. There might be an obstacle directly ahead of you on the pavement, but you won’t hit it because the car will turn with the road. This means that your emergency braking system needs to be aware of the steering, the road layout, and the expected route.

I thought this as well, but I think it emerged in an Waymo interview that any weird thing that can happen on city street can also happen on a freeway and the reaction time is lower and the consequences higher on a freeway.

Freeways have some of the same challenges as streets, but not all of them. Treating the environment as if anything can happen at any time is just an "abundance of caution" thing. To use a real example, you don't get people walking up and throwing an egg at the side of your vehicle on controlled access freeways.

Rocks, not eggs, and top of vehicle, not side:

https://cphpost.dk/2016-08-26/news/more-rocks-being-thrown-f...

Yeah, that's a different thing.

Like many people, you are focusing too much on the easy case and neglecting the many, many edge cases.

Whenever I drive on highways in heavy rain I wonder how a self-driving car would behave. Virtually all human drivers drive unsafely in these conditions by following too closely. Would a Waymo keep the distance? Seems difficult to do in heavy traffic. The alternative I guess is to drive very slowly.