Pray tell how a Lidar prevents crashing in this situation?

Accurately determine distance to objects in almost no time. While a human has 1 second reaction time. There will be situations a fast reaction time alone can save.

Pile ups happen because people drive:

- Over the speed limit (it's called a limit for a reason)

- Too fast for the conditions (speed limit != speed target)

- Too close to the vehicle in front of them

There are very few situations that can't be prevented by driving properly in the first place.