at speeds of or greater. The first high-speed rail service was the Japanese Shinkansen, which entered service in 1964. In the following decades, high speed rail networks were developed across much of Europe and Eastern Asia, providing fast and reliable service competitive with automobiles and airplanes. The first high-speed train in the Americas was Amtrak's Acela in the United States, which entered service in 2000. To the present day Towards the end of the 20th century, increased awareness of the benefits of trains for transport led to a revival in their use and importance. Freight trains are significantly more efficient than trucks, while also emitting far fewer greenhouse gas emissions per ton-mile; passenger trains are also far more energy efficient than other modes of transport. According to the International Energy Agency, "On average, rail requires 12 times less energy and emits 7-11 times less GHGs per passenger-km travelled than private vehicles and airplanes, making it the most efficient mode of motorised passenger transport. Aside from shipping, freight rail is the most energy-efficient and least carbon-intensive way to transport goods." As such, rail transport is considered an important part of achieving sustainable energy. Intermodal freight trains, carrying double-stack shipping containers, have since the 1970s generated significant business for railroads and gained market share from trucks. Increased use of commuter rail has also been promoted as a means of fighting traffic congestion on highways in urban areas. Types and terminology Trains can be sorted into types based on whether they haul passengers or freight (though mixed trains which haul both exist), by their weight (heavy rail for regular trains, light rail for lighter rapid transit systems), by their speed, and by what form of track they use. Conventional trains operate on two rails, but several other types of track systems are also in use around the world. Terminology The railway terminology that is used to describe a train varies between countries. The two primary systems of terminology are International Union of Railways terms in much of the world, and Association of American Railroads terms in North America. Trains are typically defined as one or more locomotives coupled together, with or without cars. A collection of passenger or freight carriages connected together (not necessarily with a locomotive) is (especially in British and Indian English) typically referred to as a rake. A collection of rail vehicles may also be called a consist. A set