Once autonomous cars are ubiquitous, it should be possible to increase speed limits substantially above where they are now, since the autonomous cars will have instantaneous reaction times.
Of course, but with instantaneous reaction times you can achieve the same stopping distance at higher speeds. If it takes one second for a driver to start braking when something happens (which is about the average) then a human driver going 65MPH will have the same stopping distance as an autonomous car going 78MPH.
