The duration between when the pedestrian collapses and when the driver runs over the pedestrian is not as relevant as you seem to be implying. If someone is standing in a crosswalk in broad daylight and falls over, even if the pedestrian collapses 0.1 seconds before someone runs them over that doesn't leave the driver blameless. Why, in broad daylight, in the middle of a crosswalk, was a driver 0.1 seconds away from running over a pedestrian? That sounds like poor road design, poor driving, or another factor. The same logic applies even as we worsen the conditions: if it was dark, where was the lighting? If the pedestrian "suddenly appeared" from behind an obstacle, why is there an obstacle that close to a road and why can a pedestrian get so close that they can "appear" from behind that obstacle?

Roads should be designed so that pedestrians cannot accidentally end up 0.1 seconds (or pick your duration) from being crushed by a driver. And drivers, state-licensed machine operators, should face an incredibly high bar of scrutiny when it comes to damaging pedestrians. Yes this probably means very different road designs than the ones we have now, that is one of the end goals of this kind of effort.