A "safe" distance between cars is defined by the reaction time of the driver, not the speed they are traveling. Nobody expects a driver to come to a complete stop in the distance available between two vehicles, just that they react quickly enough to not rear-end the vehicle in front. For autonomous cars traveling in a "pack" mode, the difference between the first car starting to brake and the last car also braking is going to be measured in small fractions of a second. Computer driven cars can also communicate how hard they are braking so they won't catch up to each other. So the vehicles can travel much closer together.

I agree that passengers want a gentle ride, however what time frame are you thinking about when you say "As of right now"? Six months? Six years? If you remove the need to sit upright and view the road ahead, there's no reason we can't lay down in seats that swivel with acceleration. If the seats can rotate so that the perceived acceleration is always "down", then you won't even spill your coffee under rapid acceleration. Time will tell and I'm looking forward to seeing what evolves.

More miles driven/ridden? Sure. However, those miles done by the 65+ crowd is probably not going to be during rush hour. Also, a lot of the longer trips are going to be done at night. Personally I'm looking forward to getting into the car in the evening, going to sleep and waking up at my vacation destination in the morning. As others have mentioned, self-driving only lanes will take care of most of the problem. That lane will be whipping along at 90+ with inches between each car.