Evidence from Scotland shows no reduction in RTAs due to dropping the limit. Because, yes, alcohol does lower capability even at legal levels but you get equal or higher impacts from things like being tired, having a child in the car, having a cold, using a hands-free phone, and so on as well as things that are illegal but not meaningfully enforced such as holding a phone or failing to ensure the vehicle is in proper condition.
I've made a similar observation in the past. As far as I'm aware previous studies have not shown that people under the current alcohol limit represent any significant increase in risk on the road. Drink driving idiots tend to go well over the existing legal limit and reducing that limit isn't going to stop them.
