Year	million ton-km
1970	0.400000006
1971	0.5
1972	0.6000000238
1973	0.8000000119
1974	1
1975	3.4000000954
1976	4.5
1977	6.5999999046
1978	6.8000001907
1979	4.6999998093
1980	0.8000000119
1981	1
1982	1.2000000477
1983	0.6999999881
1984	1
1985	0.8000000119
1986	0.6000000238
1987	0.6000000238
1988	0.6999999881
1989	0.8999999762
1990	0.8999999762
1991	1.3999999762
1992	1.6000000238
1993	2.9000000954
1994	3.2999999523
1995	3.5
1996	3.5
1997	3.9000000954
1998	3.5
1999	0.8000000119
2000	0.8
2001	0.798
2002	1.246
2003	1.176
2004	1.289
2005	1.364
2006	1.601
2007	1.438
2008	1.589
2009	1.384
2010	0.554163455
2011	0.509
2012	0.317003019223559
2013	0.005484
2014	0.005484
2015	0.005467548
2016	0.007249968
2017	0.0108797367
2018	0.0108797367
2019	0.00246400383690811
2020	8.624E-05
2021	0.000590054