What value do we put on a life?
It's a very interesting question and far too complex for simple numbers that governments try to put on things.
Risk is highly subjective. If we put a multi-million dollar cost per life when thinking about medicines for example, things get very costly. Latest figures (2017) gave about 25000 new cancer patients in NZ. Admittedly not all will be at risk of death, but you could suggest that untreated, they may all be. At $4m per life that is $100bn which is four times the health budget - just for cancer patients (this is obviously over-simplistic). You can do similar numbers looking at the NZTA spend against 350 fatalities per year. Individual projects stack up, perhaps, but a higher level view may not.
But if you look at a probabilistic analysis, a widely used 'broadly acceptable' limit for workers is 1 in 100,000 risk of fatality per year. A cost benefit analysis would suggest $4m is too low. In my view, anyway, but as I say, it is very subjective.