I think US speed limits are so low in part because of an effort to limit demand for oil in 1973; see Wikipedia.
Even setting aside that ignominious origin, I expect that optimal speeds have significantly increased as technology has improved and so speed limits are probably too low because of inertia.
This assumes speed limits were correctly calibrated at some point. I think the actual cost of road deaths (which are arguably the top single cause of QALY loss even at current historically low rates) is high enough that I suspect it was originally set way too high and is still unreasonably high given the costs.
I think US speed limits are so low in part because of an effort to limit demand for oil in 1973; see Wikipedia.
Even setting aside that ignominious origin, I expect that optimal speeds have significantly increased as technology has improved and so speed limits are probably too low because of inertia.
This assumes speed limits were correctly calibrated at some point. I think the actual cost of road deaths (which are arguably the top single cause of QALY loss even at current historically low rates) is high enough that I suspect it was originally set way too high and is still unreasonably high given the costs.