[quinthar]

I think a big challenge (and perhaps the root problem) is weighing the relative importance of different relative changes. Car deaths are down 97%, but suicides are up 30%. On balance, are things getting better or worse? (I'd say that car deaths are by far more common so the reduction there is more significant, but suicides are probably more directly correlated to happiness that car accidents...)

I'm more persuaded by the optimistic perspective, personally, but these are great contrasting pieces to highlight that it's not a slam dunk.

[dredmorbius]

The biggest reduction in car deaths per passenger mile occurred from 1915-1925, about a halving in a decade.

Since then, from 1925 - 2015, the rate has consistently halved every 20 years.