Year	Number
1970	11500000
1971	11300000
1972	11900000
1973	12500000
1974	13100000
1975	13700000
1976	14600000
1977	15400000
1978	15900000
1979	18100000
1980	18700000
1981	19300000
1982	19900000
1983	20700000
1984	22500000
1985	21800000
1986	25400000
1987	26500000
1988	27200000
1989	27400000
1990	27600000
1991	27600000
1992	27700000
1993	28300000
1994	29200000
1995	30500000
1996	31600000
1997	32400000
1998	34000000
1999	33600000
2000	33800000
2001	34100000
2002	33400000
2003	33500000
2004	35600000
2005	36500000
2006	38600000
2007	40900000
2008	43500000
2009	45100000
2010	46900000
2011	48100000
2012	48600000
2013	51700000
2014	50300000
2015	48900000
2016	48300000
2017	49200000
2018	49600000