Genuine question, how many lives were saved by the fuel efficiency? Does it cancel out? That is to say how does this compare to the number of lives worth of man

Genuine question, how many lives were saved by the fuel efficiency? Does it cancel out? That is to say how does this compare to the number of lives worth of man hours saved in fuel costs? It’s the same logical trade off of speed limits and cars in general, raising the speed limit costs lives but if it saves more man hours worth of lives than lives it costs it’s worth it.