There is a link to the original study in PDF format within the AAFP article.

Alcohol/Energy Drink Combo Leads to Higher Intoxication, Driving Risk — AAFP News Now — American Academy of Family Physicians

“Caffeine appears to reduce subjective perceptions of alcohol intoxication, but it does not ameliorate the performance deficits produced by alcohol,” said Thombs. “(Individuals) are more alert but just as behaviorally impaired as if they did not consume caffeine.”