Is it possible for car to do some calibration of some sort to decide what is current "sensor visibility"? Like a human would do in a fog. Is this a common practice to use this information to reduce or alter speed of the car?
At the end of the day, you can drive only as fast as your perception capabilities. A good example of that is how fast humans can perceive when influenced by drugs/alcohol/medications vs. when uninfluenced.
What is baffling is the fact that the car was driving at 38 mph in a 35 mph zone. This should not happen regardless of how well/poor your sensing/perception capabilities are.