On absolutely straight roads there might be marginal use for radar but it certainly is dangerous to not drive very cautously under conditions of low visual perception.

While a good number of drivers have the common sense to slow down in the fog and conditions of low visibility,a large number do not and in the UK and other parts of Europe they cause pile ups and deaths on fog bound motorways every year; people also get killed here when they drive into fallen trees in the dark so the radar would provide a warning to people in these cases.Doing nothing about this problem is not an option.

They are called "Driver Assist Systems" and Audi already has them.

"Do something" -- stop driving.

Yes, "doing nothing" is an option. Every action has costs (risks) and benefits; we need to balance costs and benefits constantly. If engineers find ways to make things better, great; but we don't NEED to address any particular imperfection in the world.

Not needed if you have the infra-red night vision camera systems now offered by some OEMs on their higher grade models. The infra0red camera atke real-time video and display it on a userfriendly screen on your console, after some image inhancing of course, to show a picture almosty as if you were driving in clear conditions during the day. it also highlights and warns of moving objects coming into the path you are traveling, such as pedestrians, bikes, or other cars. Currently only one of the systems gives you such a clear definition and also does not blind you when cars come the other direction with their headlights on full. Check with your car dealer.