from over 1,100 million tons in 2008 to 687 million tons in 2018. The fastest growing rail traffic segment is currently intermodal. Intermodal is the movement of shipping containers or truck trailers by rail and at least one other mode of transportation, usually trucks or ocean-going vessels. Intermodal combines the door-to-door convenience of trucks with the long-haul economy of railroads. Rail intermodal has tripled in the last 25 years. It plays a critical role in making logistics far more efficient for retailers and others. The efficiency of intermodal provides the U.S. with a huge competitive advantage in the global economy. A major factor in making U.S. rail intermodal freight competitive is the use of double-stack rail transport, where shipping containers are loaded two-high on special freight cars, potential doubling the number of containers one train can carry, with corresponding reductions in operating costs. Freight rail working with passenger rail Prior to Amtrak's creation in 1970, intercity passenger rail service in the U.S. was provided by the same companies that provided freight service. When Amtrak was formed, in return for government permission to exit the passenger rail business, freight railroads donated passenger equipment to Amtrak and helped it get started with a capital infusion of some $200 million. The vast majority of the 22,000 or so miles over which Amtrak operates are actually owned by freight railroads. By law, freight railroads must grant Amtrak access to their track upon request. In return, Amtrak pays fees to freight railroads to cover the incremental costs of Amtrak's use of freight railroad tracks. Passenger railroads The sole long-distance intercity passenger railroad in the continental U.S. is Amtrak, and multiple current commuter rail systems provide regional intercity services such as New York-New Haven, Stockton-San Jose and West Palm Beach-Miami. In Alaska, intercity service is provided by Alaska Railroad instead of Amtrak. Commuter rail systems exist in more than a dozen metropolitan areas, but these systems are not extensively interconnected, so commuter rail cannot be used alone to traverse the country. Commuter systems have been proposed in approximately two dozen other cities, but interplays between various local-government administrative bottlenecks and ripple effects from the 2007–2012 global financial crisis have generally pushed such projects farther and farther into the future, or have even sometimes mothballed them entirely. The most culturally notable and physically evident exception to the general lack of significant passenger rail transport in the U.S.