The railway as a means of transport is a very old idea. At its beginnings, it was mainly utilised in the central European mines with different means of traction being applied. But it did not come into general use until the invention of the steam engine. Since the 18th century it has developed faster and faster until in the 21st century it has become the most efficient means of transport for medium distances thanks to the development of High Speed.
The main factors that have driven the enormous development of the railway, as any other means of transport, have been, and continue to be safety, speed and economy. On top of all this, as every day passes, its environmental impact is minimum, if not zero. In the case of the railway, one of the determining factors behind its development was the type of track used, either because of its gauge or the materials used in its construction. At the start, these were made of cast iron, but they turned out to be lacking in safety as they easily broke due to their fragility. Towards the end of the 19th century steel began to be used as it was a less fragile and much stronger material. Nowadays, plate track is a key element in the development of High Speed trains making wooden sleepers a thing of the past. The rubber track mountings which are currently used to support the tracks have led to enormous reductions in vibration and noise both in the track and the rolling stock. Moreover, each country had a different track gauge due to strategic reasons of commerce and defence. Today's global markets leave no other option but to standardise track gauges or failing that, to produce rolling stock that can be adapted to the different gauges quickly and automatically.
The birth of the railway is linked to the birth of the steam engine, while the tremendous development of the railway in the 20th century was linked to the electrification of the railway lines. In addition, the diesel locomotive played a very important role because of its autonomy, particularly on those lines where electrification was unviable. The rivalry between these three types of locomotive was long and hard with each competing to see which was the safest, fastest and cheapest. The first electric locomotives appeared in the last third of the 19th century, while the first Diesel locomotive was built at the beginning of the 20th century (Faure, 2004). Diesel locomotives never reached the speeds of electric locomotives; however, the latter require a greater investment in infrastructure to electrify the line. As we all know, it is electric locomotives that are at the forefront of railway traction, while the Diesel locomotive is kept for some very specific uses. The final decade of the 20th century and the first decade of the 21st century were marked by the enormous rise in High Speed due to the huge leaps forward in electric locomotive technology.
After this very brief historical introduction, in this chapter, we will now focus on the different types of railway traction and their importance in the development of the railway, with particular reference to safety, speed, economy and environmental impact. The basic aim is to give a detailed description of how the most generally used traction and engine systems work in present-day railways. An analysis of the critical or least efficient points of the way they work will lead us to discover the main criteria for optimising railway traction systems. This could be a starting point for conducting research and seeking innovations to produce ever more effective and efficient traction systems. The final part of this work will suggest and justify some ideas that could be useful for improving the operating efficiency of railway traction systems.
In order to fulfil the objectives described in the above paragraph, a methodology will be applied that is based on the consideration of physical models that represent the behaviour of the railway traction systems under study, taking account of all the processes of transformation, regulation and use of energy and even being able to recover it. Special attention is placed on the elements that can lead to losses of energy and efficiency. Specifically, these models are developed using the Bond-Graph technique. This technique is widely accepted for its capacity to model dynamic systems that embrace various fields of science and technology. Modelling is performed systematically in a way that enables all the dynamic, mechanical, electrical, electromagnetic and thermal phenomena, etc, that may be involved, to be taken into account. Moreover, this technique has more than proven itself to be suited to modelling vehicular and rail systems. By taking the corresponding conceptual models, the Bond-Graph models are generated, and, by means of very mechanical procedures the behaviour equations of the dynamic systems can be found. By then taking these behaviour equations or mathematical models, computer applications can be built to simulate, analyse and validate the behaviour of the developed models.