Ah, but they don't have to stop, do they? Unless a whole group of people starts crossing the road all at the same time and holding hands (in which case, well,

Ah, but they don't have to stop, do they? Unless a whole group of people starts crossing the road all at the same time and holding hands (in which case, well, you can't stop people from committing mass suicide I guess), even a very rapidly moving car should be able to swerve out of its way to avoid a pedestrian walking across a motorway, so long as it detects said pedestrian at a sufficient distance. If you assume that the self-driving cars talk to each other, then each has access to the sensors of the cars far ahead in front, so even in busy traffic they should be able to detect a pedestrian standing by the side of the motorway and start adjusting their flow accordingly, well ahead of any drunken stumbling by said pedestrian. Unlike human drivers, cars can adjust their trajectories at high speed with minimal risk of accident.