Year	Number
1970	34700000
1971	35200000
1972	35600000
1973	35700000
1974	35600000
1975	35400000
1976	34900000
1977	34400000
1978	33600000
1979	32900000
1980	32400000
1981	32000000
1982	31600000
1983	31600000
1984	31900000
1985	32500000
1986	33300000
1987	33900000
1988	34400000
1989	34900000
1990	35100000
1991	35300000
1992	35400000
1993	35600000
1994	35800000
1995	36300000
1996	36500000
1997	37100000
1998	38000000
1999	39100000
2000	39700000
2001	40500000
2002	40700000
2003	40100000
2004	37900000
2005	36300000
2006	35100000
2007	34000000
2008	32500000
2009	31600000
2010	30800000
2011	30100000
2012	29400000
2013	31400000
2014	31300000
2015	30900000
2016	31100000
2017	32000000
2018	32400000