In which case the number should be multiplied by the percentage of cases it can be activated in, if you can Level 3 self drive in, eg "up to 37 mph but only on highways" so you multiply 3 by 0.001 because it's only useful in 0.1% of conditions, and then you can add that to the times level 2 works.
That's not possible to calculate because the total denominator of possible "cases" approaches infinity. Level 3 doesn't define what the cases for operation are, that is up to each individual implementor of such a system to define. The criteria is likely to be more much more complicated, like "the output of all 12 sensors when applied to this algorithm, and referenced against this mapping data, delivers a confidence greater than x"
Things don't really get that simple until level 5.
Even at level 4, we're going to have vehicles that pull over when they can't figure out how to navigate successfully.
It's a useless number for consumers then, a Level 3 system could be way less safe/useful than a Level 2 system, because it only works on a sunny day in slow traffic with other cars for reference on a highway
