Year	million ton-km
1977	4.0000000149
1978	6.8999997973000005
1979	7.6999999881
1980	7.8999999165000006
1981	9.3999999165
1982	7.500000052200001
1984	15.000000350199999
1985	16.699999861400002
1986	17.499999918
1987	17.499999918
1988	26.399999544
1989	18.1999999732
1990	18.1999999732
1991	20.3000003547
2010	25.961855596
2011	25.3690837157509
2012	26.616839581407092
2013	32.40599862
2014	32.720170859999996
2018	33.59550220996578
2019	32.455516522582755