Subway. A wide variety of high-speed transport systems makes it difficult to unambiguously classify them. All definitions are conventional underground. For many of the transport system is safe to say that they are (or, conversely, are not) underground, but at the same time there are a number of "borderline" and "hybrid" transport systems. The final decision as to include a particular transport system to the subways or not, depends on the accepted definition or can be made empirically. For example, in Serfaus and Novy Afon, there are underground railways, which have some resemblance to the underground metro lines, and therefore are often informally referred to as well. The main features of the underground in 1981, the Committee of UITP Metro proposed a definition of "railway metropolitenovskoy": "Railroad, designed to be an integral part of the network, which allows to transport large numbers of passengers within urbanized areas by vehicles on the track with an external control, being in space wholly or partly located in the tunnels and completely given over to such use. " In cities with the existing building line of the metro, usually laid underground and occasionally come to the surface or on the dock. Dimensions and weight of rolling stock can reach railway standards, but usually inferior to them. Metros comprise usually 4-8 cars. Diameter tunnel reaches 5-6 meters (but in many systems, there are also more narrow tunnels, such as the width of the narrow profile Berlin tunnels - just 2.3 meters), the marginal slopes than on the railways of general purpose, but less than a tram minimum radii of curvature much larger tram. Platforms at stations usually have a length of 100-160 m and a width of 5-20 m underground lines usually run along the city-axes are the framework of urban passenger transport system. The cost of construction of underground vary depending upon construction. The typical cost of a kilometer underground line shallow - about U.S. $ 30 million (excluding the cost of the construction of stations). In different countries, and performance parameters can be varied underground (for example, are almost entirely terrestrial systems), but the distinctive features are the use of underground electric traction, high intensity and speed of the trains and the large ridership. Dimensions of subways in the range of 2-km line. high-speed transport systems