Year	million ton-km
1970	0.8000000119
1971	0.8999999762
1972	0.8999999762
1973	1.8999999762
1974	1.8999999762
1975	1.8999999762
1976	2
1977	2
1978	2
1979	2.0999999046
1980	1.2999999523
1981	1.1000000238
1982	1
1983	1.1000000238
1984	1.2999999523
1985	1.3999999762
1986	1
1987	1.1000000238
1988	1.2000000477
1989	1.7999999523
1990	3.5999999046
1991	3.5999999046
1992	6.8000001907
1993	3.7999999523
1994	7
1995	9
1996	9
1997	9
1998	0.400000006
1999	0.5
2000	0.535