In 1968, a U.S. railroad’s freight train made up of 500 coal cars traveled from Iaeger, West Virginia to Portsmouth, Ohio. It had six locomotives, three pulling and three pushing. The train was 6.5 kilometers long. This world record stood until 1989, when a South African freight train consisting of 660 wagons (each loaded to some 106 tons) was moved by nine electric and seven diesel-electric locomotives. This train was 7.3 kilometers long and weighed 70,500 tons excluding locomotives which were distributed along the train. It traveled a distance of 861 kilometers in 22 hours and 40 minutes!
Longest trains (Wikipedia)