What were the different states' policies on licence revocations for grossly intoxicated motorists at the time, and how did those policies change? If the states that put in the 0.08 standard simultaneously made harsher their policies for dealing with drivers who were above 0.10, the reduction in fatal crashes by those who habitually drive severely intoxicated could easily account for the entire observed phenomenon.
"the reduction in fatal crashes by those who habitually drive severely intoxicated could easily account for the entire observed phenomenon."
I would offer that the study showed that reduction applied to both and it took a harsher revokation/suspension penalty to be used in combination.
I think it shows that both used in comination with each other reduced the deaths. It appears that you aim to say it was punishment alone that accomidated the reduction and that would be as untrue as to say that reducing from .10 to .08 casued the reduction alone.
Major problems require multiple pronged approaches to effectively deal with them.
I think the study(ies) show quite conclusive backing that this was effective. I would offer that further reduction to a .06 or lower would not have the same effect as the drop toi .08 did. But that is just imho.