Humans have this problem because they get distracted and have slow reaction times. Emergency breaking can typically stop a car within about 100 yards even from

Humans have this problem because they get distracted and have slow reaction times. Emergency breaking can typically stop a car within about 100 yards even from freeway speeds. But a distracted human might travel more than that before they even realize they should be trying to stop. Humans are also pretty bad at adjusting to conditions, so if weather makes the road slick (wet or icy) or they have limited visibility, they don't often slow down enough to compensate. Autonomous cars have none of these problems, so aren't likely to ever run in to a "can't stop in time" situation. I can't actually think of any situation where, in the event of a likely collision, the best solution isn't to just try to stop. Even if, for some reason, you can't stop quickly enough to avoid the collision, any reduction in speed will result in a reduction in the severity of collision.