# Efficient Railway Turnout Design: Leveraging TRIZ-Based Approaches
## 1 Introduction and Overview
France had been maintaining maximum speeds of 200 km/h on some of its most famous express trains (Capitole, Mistral); at the same time, it had carried out many experiments in the field of high-speed trains and has, thus, held the world speed record (330.9 km/h) since 1955, maintaining the privileged position required to make significant progress. Encouraged by Japan's success, France created a new line in the form of a railway motorway, where the speeds for which their industry had equipped locomotives and towed equipment could be developed [4; 5]. Thus, the second milestone came about as a result of the development of high-speed railways in the 1970s in France by the SNCF (Societe Nationale des Chemins de Fer Francais) with the construction of the TGV Sud Est line. In May 1990, a TGV-Atlantic composition broke the world speed record by reaching a top speed of 515.3 km/h. Another record was a run of 501 km/h through a turnout on a direct track. These new speeds imposed geometrical characteristics on the layouts, which logically included the turnouts, and, in particular, the switches. Problems arose because the turnout of a high-speed train requires very long switch rails and very wide radii. Therefore, high-speed railways have brought to light the design of much more complex and higher performance turnouts, since, in a conventional turnout, at the crossing of the frog between the two layouts, the train wheel has to pass through a section in which there is no rail, which causes the biggest problems in the turnouts. Figure 3: Schematic diagram of a turnout. Figure 4 shows an actual turnout suitable for use on high-speed railways, on which the complexity of the turnout can be seen. Switch types can be classified according to the type of rail and the characteristics of their switches and stock rails. Switch rails can either be articulated switch rails or elastic switch rails. Their layout can be secant to the direct track conductor wire on former turnout type A, as well as on type B with a radius of 320 m, or tangent on types C, V and AV, as well as on type B with radius of 500 m.  
Among the first changes that were made was the Vignole type, which corresponded to the articulated switch rail typology, in which the articulation is achieved by means of a loose joint, which did not sufficiently tighten the flanges. Its main advantage was the use of complete switch rails without any machining, which makes it very robust. However, it also has major drawbacks. On one hand, the poor behaviour of the switch rail joints (bolts, pins or loose joints) was a frequent cause of breakdowns and accidents. On the other hand, the impossibility of avoiding derailment in the event of a train taking the heel block, for which the switch rails were not properly positioned, was a serious problem [7; 8]. In terms of wear, the INSERT type crossing [9] is a successful solution. It is based on rail sections welded to a manganese steel casting insert. The use of a manganese steel insert in this type of crossing makes it possible to take advantage of the special properties of the material and concentrate them in the sensitive area in which the wheel of the rolling stock jumps. On the other hand, recent technologies have developed new ways to solve these problems, as well as the bumps with the rail, by creating elastic switches (Figure 4) and movable cores and wing rails (Figure 5) that are perfectly joined to the rail, giving more stability to the assembly so that, to avoid the crossing gap, swing nose crossing turnouts can be used, which have movable parts in this area that allow the continuity of the tread to be complete in both paths along the whole turnout (Figure 6). Figure 4: High-speed turnout, reprinted with permission from Ref. [6], voestalpine Railway Systems. The swing nose crossing was developed to address the drawbacks of fixed crossings, such as bumpy and jerky wheel over-run and transversely accelerated wheelsets, as well as the resulting high strain on components.