Analysis of Moving Autoblock System (MAS) and Its Computer Simulation Method
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Transactions on the Built Environment vol 18, © 1996 WIT Press, www.witpress.com, ISSN 1743-3509 Analysis of moving autoblock system (MAS) and its computer simulation method W. Xishi, N. Bin, L. Yun, Z. Ming Department of Communication and Control Engineering, Northern Jiaotong University, Beijing, 100044 P.R. China Abstract With rapid development of electronic and computer techniques, the autoblock systems to control train operation in blocks is towards moving autoblock system (MAS) instead of fixed autoblock system (FAS). It is emphasized that MAS can enhance the carrying capacity of railway transport. In the paper, the advantages of MAS are analyzed, which includes the elastic dispatching for the different trains with different speed, density and weight, calculation of block carrying capacity, station carrying capacity. By comparison, it is pointed out that MAS can increase the capacity by 20% — 30% to FAS. An example of capacity calculation is given in the paper. Finally, the method which can be used for computer simulation to show the performance of MAS is described as well. 1 Introduction The overall task of railway signalling control is to improve transport management and organization by raising transport efficiency and providing various kind of operation information, on the condition of ensuring train operation safety. Fixed autoblock system (FAS) was invented at the beginning of this century. To some extent, it has been played an important role in ensuring train operation safety and raising transport efficiency. However, it is not a perfect system. There exists potential in the aspect of transport organization. In the 1960s, the author of the paper put forward the idea of moving autoblock system (MAS) and some of experiments about MAS were carried out. In the past decades, development and research on MAS were carried out very quickly in many countries, such as ATCS, ARES, LZB, ETCS, CARAT etc. In terms of hardware structure, they are towards MAS. In particular, LZB system has already had the condition of MAS implementation. There is only transport organization to be done in order to have the functions of MAS. Transactions on the Built Environment vol 18, © 1996 WIT Press, www.witpress.com, ISSN 1743-3509 268 Computers in Railways Since Chinese Railway has its own transport characters, for many years, research on MAS has been conducted with more interest in varying degree. It is believed that MAS must bring about the great benefit to transport. The possible benefits of MAS are analyzed in the paper, and the computer simulation method is described. 2 Elastic dispatching of MAS for trains with different speed, density and weight In transport organization, Speed, density and weight of train are the three important indexes to reflect transport efficiency. Under the condition of FAS, it is difficult to balance the three indexes at the same time. It is very common to neglect one or two indexes for some of indexes. However, in practice, it is required that speed and density of trains are emphasized in certain sections in certain periods, while other indexes are emphasized in other section in other periods. In other word, it is required that elastic dispatching for trains with different speed, density and weight is implemented. It is very limited that elastic dispatching is implemented by FAS. The mam reason for this is that the position of wayside signaling is fixed in FAS. There are two methods to locate fixed wayside signaling in FAS. The first method is that the position of signalling is determined by the interval time of train operation strictly according to train traction curve in which the type of locomotive, haul-weight and train speed are fixed. The second one is that train braking distance is used to locate the signaling position based on train traction curve. The two methods are very similar, and both with advantages and disadvantages. The figure 1 shows the first method which are used to locate the signaling position by Chinese Railway and other country railways in the world. According to the interval time of train operation, the down-triangle is used to locate the position (Figure (a)). From the figure, it can be seen that the wayside signalling position is fixed as long as traction curve and interval time of train operation. However, in reality, there are passenger trains with different speed and freight trains with different weight running on the same tracks, and the type of locomotives are different. In the figure 2, TV1 indicates the traction curve of Twl in the figure 1. TV2 and TVS are respectively the traction curve of heavy-haul train Tw2 and the traction curve of passenger train Tw3 with higher speed If the same interval of train operation is given, the location of signalling are totally different. It means that if the location of signaling is determined by TV1, the carrying capacity of the block must be decreased when heavy-haul trains or higher speed trains run on the line. But, there no exist such disadvantage for MAS Because different trains can run in blocks according to their traction curve under the condition of MAS, and the only limitation for these trains are their running speed Transactions on the Built Environment vol 18, © 1996 WIT Press, www.witpress.com, ISSN 1743-3509 Computers in Railways 269 ca i"• \ v 'i . 'i !' i ! . - A- 1 *• ?. 9d 1 °_ fij o_ JM_ 0.3 b 2.0 1200 HGO 1200 Ino 1870 1%40 2000 1?00 T230"l750 no Figure 1 'IV, TV, hP _ _ Jo. __ Jfl. _. Figure 2 Vobjma.x = min ( Vt, V,, V,, B ) (I) In the above expression, \\ is train construction speed; V^ is permissive line speed; V<. is speed limitation for switch areas and special sections, or other temporary speed limitation; B is braking capacity. According to the traction calculation regulation of Chinese railway [3], a general dynamic model of train operation can be obtained on the condition of MAS as follows: Transactions on the Built Environment vol 18, © 1996 WIT Press, www.witpress.com, ISSN 1743-3509 270 Computers in Railways dv ^ F(t,v) - w(t, v) - B(t , v} dt. (p + G) V(to) = Vo t>to (2) V^_, = mm ( V,, V,, V,, B ) 0< V < V,^a, Among the above formula, F is tram traction force, V is real speed of train, W is various of resistance in train operation, G is train traction mass, P is locomotive calculation mass. When a train is hauled by two or more locomotives, P is the sum of each locomotive calculation mass. The formula (2) shows that train operation can be adjusted by G, P and Vobjmax- In order to enhance carrying capacity, elastic dispatching among train speed, density and weight is a key issue. Statistics for Chinese Railways in the past thirty-five year has also shown that new lines only contribute 25% to the increased carrying capacity and the rest of 75 % is relied on upgrading of the existing lines. During this period, the operation mileage of the new line is the 130% of the operation mileage of the existing line. It is obvious that carrying capacity enhancement is obtained mainly by transport organization improvement. Signaling system upgrading has been played an important role in carrying capacity enhancement. Elastic dispatching among train speed, density and weight is one of the best methods to improve the existing signaling system. The application of MAS become more and more important. 3 Comparison of block carrying capacity between FAS and MAS For FAS with three-aspect, the distance interval ( L^i ) of the two following trains can be shown in the figure 3 a. It can also be expressed by the following formula [4,5]: Lgni = 3 Ls,, + L,/2 + L,/2 (3) among the above formula, L^ is the length of each block section and all of block sections are equal. L, is train length. It is obvious that the shorter the length of block section is, the bigger carrying capacity However, the L^ can not be smaller than train braking distance. There is different braking distance with different train in the same section. For example, braking distance of passenger train will increase with its speed increase. On the condition of ensuring train operation safety, FAS Transactions on the Built Environment vol 18, © 1996 WIT Press, www.witpress.com, ISSN 1743-3509 Computers in Railways 271 with four-aspect is used to enhance transport efficiency in many countries, shown in the figure 3b in which L^,y is the interval distance of freight trains with lower speed and shorter braking distance, and L%,y is the interval distance of passenger trains with higher speed and longer braking distance. They can be expressed as follows: I/B.V = 3 L'SB + L,/2 + IV2 ] f (4) L'BIV = 4 Us,, + L,/2 + L-,/2 J LSD — Hu/2r- ^H' ,Lt/ k2 LSD — Figure 3 From the above formulas, it can be seen that the four-aspect system is better than the three-aspect system in terms of adaptability to different kinds of trains when safety and efficiency of train operation are considered at the same time. The trend is clear that the more the aspect is, the bigger the carrying capacity. That is the reason why the five-aspect system is used in the world But, on the other hand, the investment on hardware could be increased greatly when the aspect increases. For example, the number of track circuit, the signalling cable and the insolation joint increase with increase of aspect. In particular, relation between wheel and rail will be deteriorated to affect train operation when the number of insolation joints increase in rails.