Preventing engaging something in bad conditions is a lot easier than what do you do if the conditions suddenly happen.

If it's suddenly foggy it needs to be able to handle the situation well.

Cameras/Lidar don't work well in fog. Radar does, but it isn't a primary sensor and can't be driven on safely alone in any circumstance.

So now you need to slow down (which humans will do) but also since the sensors are failing or insufficient, safely get out of the way of what might be other incoming vehicles behind you, or slow/stopped vehicles ahead of you.

You could restrict hours the system can be engaged which will reduce the likely hood of certain events (e.g morning fog, or sunrise/sunset head on sun) but there's still unpredictability.