We can’t assume the change in drinking age was the sole cause of reductions in DUI. There was a major cultural change during that same era in regards to DUI, in the 70s and early 80s there was an assumption of drinking and driving, drinking while driving even. I had neighbors that judged driving trips by 6 packs, and nobody thought it was a big deal, it was just how things went. We don’t think that way anymore, plus there’s much more draconian DUI laws to make sure even the people that want to think that way don’t. And vehicle technology has improved dramatically making crashes safer. I doubt there will be any increase in DUI fatalities with a lower drinking age, the drinking age really doesn’t prevent drinking by the young, it just moves it to darker corners of the world.
Unless they're illegal aliens ...