Have better safety measures, tougher enforcement, and the use of designated drivers caused the reduction in traffic deaths?

"After the age-21 MLDA was implemented, alcohol-involved highway crashes declined immediately (i.e., starting the next month) among the 18- to 20-year-old population. Careful research has shown declines are not due to enforcement of and tougher penalties for driving while intoxicated, but are directly a result of the legal drinking age." (Wagenaar, A. C., & Toomey, T. L. (2002). Effects of minimum drinking age laws: Review and analyses of the literature from 1960 to 2000. Journal of Studies on Alcohol, Supplement 14, 206-225.)

An article published in 2008, considered one of the most comprehensive and rigorous of studies on the minimum legal drinking age, revealed an 11 percent drop in alcohol-related traffic deaths among those under age 21. Authors point out that this may be a conservative figure, and the effect could actually be higher. (Fell, J.C., Fisher, D.A., Voas, R.B., Blackman, K., & Tippetts, A.S. (2008). The relationship of underage drinking laws to reductions in drinking drivers in fatal crashes in the United States. Accident Analysis & Prevention, 40(4), 1430-1440.)