used for the fastest trains introduced after 2000, exceeding 300 km/h. Shanghai Transrapid is one example, with a line speed of 430 km/h. Ultra high-speed rail Generally, the speed range for ultra high-speed rail is between and . A number of both technological and practical variables begin to influence trains in the vicinity of 500–600 km/h. Technologically, the limitations are by no means beyond reach, however conventional trains begin to encounter several physical obstacles, most notably track damage and pantograph limitations. It is important to note that the current world record for rail vehicles is held by the TGV V150 set on 15 April 2007 at , and conventional trains may indeed eventually reach into ultra high-speeds. However, this test has shown that speeds over 500 km/h are unrealistic for regular usage; it wears down the material too much. Based on current and foreseeable technology, these speeds will more than likely be reached predominantly by maglev trains. The two most prominent maglev trains are the Transrapid with a maximum speed of and the Japanese MLX01, which holds the world land speed record for rail vehicles at . Trains faster than will exceed the speed of most propeller-driven aircraft. Regardless of technological parameters, the track for such a train and anything faster would more than likely require turn radii of significantly higher proportions than current dimensions, essentially preventing anything but a direct line between terminals. Such trains are extremely unlikely in the current or near future. Greater than 1000 km/h (621 mph) Depending on the aerodynamic design of the vehicle and various ambient atmospheric conditions, a train would begin to exhibit transonic airflow in the vicinity of Mach 0.8 (988 km/h) and higher. From a modern perspective, this is essentially the realistic maximum speed of trains as they are known today. This is because the Prandtl-Glauert singularity would cause catastrophic damage to the vehicle as the sound waves reflected off of the ground, potentially blasting the train into the air. The only trains that could exceed this speed significantly are vactrains. Rail terminology with respect to railway track gauge Approximately 60% of the world's existing railway lines are built to the standard track gauge where the distance between the inside edges of the rails of the track is (see the list of countries that use the standard gauge). Narrow gauge railways have track gauges of between and . They are cheaper