Monthly total deaths and serious injuries on UK roads: Jan 1975 -- Dec 1984. In February 1983, new legislation came into force requiring seat belts to be worn.
Source
Makridakis, Wheelwright and Hyndman (1998) Forecasting: methods and applications, John Wiley & Sons: New York. Chapter 8.
Examples
plot(ukdeaths)
seasonplot(ukdeaths)
tsdisplay(ukdeaths)