Drunk Driving Fatalities Listed below are annual fatality rates (per 100,000 population)

from drunk driving. The first entry represents the year 1991. Is there a trend? Any explanation?

6.3 5.5 5.3 5.1 5.1 5.1 4.8 4.6 4.6 4.7 4.7 4.7 4.5 4.5 4.6 4.5 4.3 3.9 3.5 3.3 3.2 3.3