According to the International Union of Railways (UIC), a Paris-based rail transport industry body, there is no standard definition of a high speed railway. Generally, a railway system designed for speeds above 25 kmph is called high speed (some sections might have a lower speed limit because of safety reasons). As on September 2014, only 15 countries have such railways. China has more than 11,000 km of high speed tracks ­ the longest in the world. Japan , Spain, France and Germany are the only other countries where tracks dedicated for high speed trains are more 1,000 km long.Japan was the first to have a high speed rail line, between Tokyo and Osaka, which became operational in 1964. The famous Shinkansen or bullet train ran on this line at a speed that could reach about 210 kmph. Italy was among the first in Europe to experiment with high speed rail lines. The first high speed line connecting Rome to Florence became operational in 1977 at 250 kmph as the top speed. The national French railway company started the operation of the first high speed line between Paris and Lyons on September 27, 1981 at a maximum speed of 260 kmph.According to the UIC as on April 1, 2015, the total length of high speed rail lines across the world is 29,792 km. Over 3,000 high speed trains run on this network carrying about 1,600 million passengers annually . China's passenger traffic of 800 million annually is the highest in the world.Most of today's high speed trains operate on conventional tracks. The system runs on tracks similar to conventional gauge but built by stronger material. The train consists of passenger cars and may be two synchronised engines (power cars) at both ends. Most of these trains get their electricity supply from roof-mounted pantographs and overhead supply lines. To support high speed, a large part of the route alignment is straight. Many of these trains can run on conventional tracks at a significantly reduced speed.Unlike conventional trains that use wheels, the Maglev system is based on magnetic lev. Electromagnets are itation. Electromagnets are used to levitate the train a short distance just above the tracks. These magnets also create the thrust that moves the train. When compared to conventional trains, Maglev has superior control as its acceleration and braking doesn't depend on friction of the track. They can also reach a far higher speed. Maglev is very expensive to construct and at present there are only three operational commercial Maglev systems, in Japan, China and South Korea.