I used to drive through the mountains of Pennsylvania along U.S. Route 322 back in the 90s when I was in college, often late at night when the road is mostly empty. Up in that section of the road it is a four-lane divided highway, and in good visibility higher speeds are quite safe.
But at night it sometimes gets really foggy, and I would slow down to around 35 mph because of the scenario you describe. If there is a truck stopped in the lane I'd smash into it.
Similar here... the Autobahn A2 is already pretty infamous for its high number of fatal accidents (because of the high traffic density, as main road between east and west europe).
But it also has the tendency in the summer, to surprise you with sudden heavy rain in the middle of nowhere (Between Peine and Hanover). From clear sight to 0 mm (windshield) in a few seconds. With braking distances increased quickly because of the water rising on the road.
When you are not keeping a good distance and already have a sane velocity, before the rain surprises you, you have no chance to slow down when you see the braking lights of the car in front of you. Or to control your car in that situation, even ABS fails when you have 2 cm water on the road.
I had a few near misses in such a situation already before, even slowing down to 30 km/h (where you can usually drive 130 km/h recommended speed or more) is no guarantee that you can really stop when you see another car in front of you.
And combine this with the fact, that right at the place, where such rainfall happens most often, you also have a very high chance for traffic jams.
The latest ruling by a court in Germany now clarified how you must behave according to laws:
Minimum distance is half your velocity (in km/h) as meters (or: velocity multiplied with 1/1000 h). Recommended distance is 1 second of reaction time + braking distance.
Braking distance is defined simple in the regulations by s = 1/4 * v * t * k.
s is the safe braking distance in meters.
v is the velocity (in km/h).
t is the time for stopping ( 1 second in town, 2 seconds out of town)
k is the factor for the road condition (usually k=1 for a dry road, k=2 for wet roads, k=4 for gravel on the road, k=8 or more for ice)
So, at 130 km/h on the Autobahn with dry road, you need to plan with 39 + 65 = 104 meters distance to stop.
Also, the judges now clarified for how long you may drive with reduced safety distance (for example, when a car enters the highway in front of you): The maximum allowed time is either the time it takes to travel 140 meters or 3 seconds, what ever is lower. Means effectively: If you drive much faster than recommended, you have to react much faster.
If you are caught trailing a car for a longer time at less than half your indicated velocity ... it gets really expensive. At 260 km/h, this means effectively less than 2 seconds to get to safe distance again.