Rush hour in major cities would be an entirely different experience with automated cars.

In my observation, the vast majority of congestion is caused by drivers either overcompensating for changes in conditions (ie slowing down even more than the car in front of you slowed down) or otherwise reacting slowly.

I believe highways could handle considerably more traffic if all the traffic were automated.

I think it's possible to see significant gains if only some of the cars were automated, actually.