The speed limit example is a great one. Consider a road that has a 35mph limit. Now - which of the following scenarios is SAFER: a) I'm driving on the road in a brand new 4x4 porsche on a sunny day with great visibility and brand new tyres. Doing 40mph. b) I'm driving on the same road in a 70s car with legal but somewhat worn out tyres, in the dark, while it's raining heavily. Doing 35mph.

Of course technically option a is violating the law but no sane police officer will give you a fine in this case. Nor should they! A robot will, however. This is stupid.

The Cayenne would be safer going 35 instead of 40 regardless of all other variables. It's a trivial physics question, kinetic energy is a function of mass and velocity.