鐵路運輸

香港港鐵翻新後的M-Train，港鐵本地鐵路路綫過去12個月的累積載客量超過12億人次，平均周日載客量達350萬人次^[1]，是全球最繁忙的鐵路系統之一。

鐵路運輸是指由任何形式的路軌引導列車的行走的一種交通工具。在狹義上通常是指一種以具有輪對的車輛沿鐵路軌道運行，以達到運送旅客或貨物目的的陸上運輸方式。而廣義的鐵路運輸尚包括磁懸浮列車、纜車、索道等並非使用車輪形式，但仍然沿特定軌道運行的運輸方式，通稱軌道運輸或軌道交通。相比起路面運輸工具，鐵路運輸被路軌所規限，不能自由行走。通常路軌是由鋼鐵製成，而且並安裝在由木板或混凝土製作的路枕上。列車的輪距需要和軌距一致。

Rolling stock in railway transport systems generally has lower frictional resistance when compared with highway vehicles, and the passenger and freight cars (carriages and wagons) can be coupled into longer trains. The operation is carried out by a railway company, providing transport between train stations or freight customer facilities. Power is provided by locomotives which either draw electrical power from a railway electrification system or produce their own power, usually by diesel engines. Most tracks are accompanied by a signalling system. Railways are a safe land transport system when compared to other forms of transport.^{[Nb 1]} Railway transport is capable of high levels of passenger and cargo utilization and energy efficiency, but is often less flexible and more capital-intensive than highway transport is, when lower traffic levels are considered.

The oldest, man-hauled railways date to the 6th century B.C, with Periander, one of the Seven Sages of Greece, credited with its invention. With the British development of the steam engine, it was possible to construct mainline railways, which were a key component of the industrial revolution. Also, railways reduced the costs of shipping, and allowed for fewer lost goods. The change from canals to railways allowed for "national markets" in which prices varied very little from city to city. Studies have shown that the invention and development of the railway in Europe was one of the most important technological inventions of the late 19th century for the United States, without which, GDP would have been lower by 7.0% in 1890. In the 1880s, electrified trains were introduced, and also the first tramways and rapid transit systems came into being. Starting during the 1940s, the non-electrified railways in most countries had their steam locomotives replaced by diesel-electric locomotives, with the process being almost complete by 2000. During the 1960s, electrified high-speed railway systems were introduced in Japan and a few other countries. Other forms of guided ground transport outside the traditional railway definitions, such as monorail or maglev, have been tried but have seen limited use.