Analysis of Moving Autoblock System (MAS) and Its Computer Simulation Method

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.

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

Computers in Railways 269

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:

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

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.

MAS, in terms of operation organization, can be adaptive to different kinds of trains to obtain the maximum carrying capacity with optimal train operation. On the conditions of MAS, the interval distance L^s of the two following trains is shown in the figure 4. It can also be expressed as follows:

L'MAS ~ -^M "•" L'R ~*~ WSB " WEB ^ W + LMASB W

* Lpse - LFRB + L, + L, + L^,, (5)

272 Computers in Railways

Oil J f. Un .L, I.MASO ' LFEB ' -T/I LM LT/J , 4 i M**.

Figure 4

among the above formula, L^ is the distance train covers during information transmission in MAS. l\ can be neglected when train speed is not high, LR is the distance train covers during the period when driver

confirms information change or on-board equipment recognizes information concerning train operation. L^u is the service braking distance required by the following train. L,.,..„ is the emergency braking distance required by the front train. L^ is the average length of trains. L^ASB ^ the buffering

distance which is the certain designed distance for adjusting to ensure train operation quality in Sections. L% is the safe interval distance after the two following trains stop.

According to the Chinese Railway Regulation [3], the following expression can be obtained:

4 . 17 ( l/f - V* ) 6 ) 3 .6 10006,,%). + O^ ^

-•FEE 3.6 E

among the above formula, and t\ are respectively equivalent virtual braking time [3].

In practice, the value L% varies with train speed. The higher the train speed

is, the larger the value L% In the light of experience, we have,

T LS = '-'FSB

K, = 0.5 if V, e [160,320] K, = 0.4 if V, e [120,160] K, = 0.35 if V, <= [80, 120] (8) 0.3 if V, e [45, 80 ] K, = K, = 0.2 if V, e [30, 45 ] K, =00.11 if V, e [0, 20 ]

Computers in Railways 273

The average value of L^ASB ^ related to train speed [5], it is,

= V, X Z [ go - Wg ( go - g, ) ] (9)

Z is the average interval time of trains, go and g, are the buffering time quotient. Wg is the probability of the event occurrence that the same group of trains are late.

In order to simplify calculation, the expression (9) can be rewritten approximately as follows:

K, = 0.5 if V, e [160,320] K, = 0.4 if V, e [120,160] BU = 0.35 if V, e [80, 120] I. (10) BL = 0.3 if V, e[45, 80 ]

K^ = 0.2 if V, 6= [30, 45 ] K, = 0.1 if V, e [0, 20 ]

When the values L^, L^ are very small and neglected, the expression (5) can also be rewritten:

LMAS ~ Lpse - Lp^g + K, Lpgg 4- K^ Lpgg + Ly

= (1 +K, + K, ) LPSB + LT - L™ (11)

When the front train has stopped, then,

p,B = 0 (V,' = 0) (12)

As a result, we have,

Min L^ = ( 1 + K, + K. ) L^ + L^ (13)

It is concluded that the mathematic model of block carrying capacity for

MAS is the expressions: (6), (7), (8), (10),(11) or (13). Compared with FAS with three-aspect or four-aspect, MAS can increase block carrying capacity by about 30% or 20% at the worst conditions. It only means the static carrying capacity in block. If transport organization is carried out reasonably, and optimized by computer, the carrying capacity in block could increase more.

4 Comparison of station carrying capacity between FAS and MAS

274 Computers in Railways

On the conditions of FAS and MAS, comparison of station carrying capacity can be conducted according to the following circumstances:

(1) Train are dispatched from stations,.shown in the figure 5(a)l and 5(b)l.

(2) (i)

J rI 3?

~Y 1-5. ) 2.'.5

0 C I In )

( G U X i. 9J_ i-v. ,

T (n)

Figure 5

(2) Trains arrive at stations, shown in the figure 5(a)2 and 5(b)2.

(3) Trains pass by stations in the same direction.

For FAS, the distance between the two following trains ( shown in the figure 6 ) LB,,," is,

,i" = 2 L,,, 4 L,,,, + L,, + L, 4 , V, (14)

Among the above formula, L^,^, is the distance between the home signal and start signal at station L is the length of the switch section at throat area of the station, and related to the number of tracks at station, tp is the confirmation time that during the period that fact has been confirmed that the arrival train has cleared the switch area, the route for the next train has been established and home signal has been cleared again.

Computers in Railways 275

L r — *— V•* *— IU/1 L« U LgB. ST LP IT/ J

Figure 6

The comparison results for the above circumstances are given in the table 1 in which L^,, in the number 2 needs to subtract the length (L^) of a block section for FAS. When the train enters the switch areas at station, it has to reduce its speed. L,^,,' is used instead of L%,,,. In the same circumstance, for MAS, the interval distance is Min L^SL when the front train has been at station, i.e. the expression (13). In the table 1, the estimated values for the comparison between FAS and MAS are given. As long as a large quantity of calculation is conducted by computer simulation, the calculation values can be obtained. The calculation relates closely to transport organization method. For example, there are the four different kinds of the following trains organization method: freight train follows passenger train, passenger train follows freight train, passenger train follows passenger train, freight train follows freight train Even for freight trains, there are different weight trains. In addition, it also relates to other factors, such as the number of tracks and the length of tracks at station.

Table

FAS/MAS No. Comparison condition FAS MAS Capacity Estimation 1 Dispatch from station L,,,,, [3] >130% LwAs,. [5] Lnm' [3] > 120-130% 2. Arrival station Min LUASL [3] (minus a L^)

Pass Station at the 3 LuASL [5] >I30% same direction LBIII

An initial analysis of carrying capacity is given by calculation values in the table 2. It is a real example in Chinese Railway. The section is from

Dezhou to Jinan on the line from Beijing to Shanghai. The total length of the section is 120.8 kilometers. The maximum gradient in the down direction is - 7.8 millimeter. For passenger train and freight train, the haul- weight are respectively 1100 tons and 3800 tons, the number of wagons are respectively 18 and 52, and the speed limitations are respectively 120 km/h and 80 km/h. According to the above conditions, the traction calculation software is applied to obtain the results of the example [6] in the table 2.

Table 2

Freight train in pairs (FP) Carrying Capacity (CC) FAS MAS/FAS Passenger train MAS (1=6)MAS (1=5) No. 3-aspect in pairs (1=8) FP CC FP CC FP CC 1 2

r 30 91 121 119 149 144 174 123% 14334

2 40 72 112 103 143 124 164 12794 146%

50 58 108 87 137 98 148 12694 137% 3 60 106 134 84 144 4 46 74 12634 13694

In the table 2, the fixed interval time (I) is used to calculate the carrying capacity of MAS. Even so, the comparison result shows that compared with FAS, MAS can still increase carrying capacity by 23% -- 43%.

5 Computer simulation method of moving block system

From the above analysis, it can be seen that MAS could enhance transport capacity. However, it depends on many factors. For example, on the one hand, it relates to railway hardware, such as station structure including track numbers and the effective length of track, stations and yards distribution including the distance between stations. On the other hand, it involves management and organization of train operation which can be called as railway software. For example, the number of the necessary passenger train and its level, the necessary train stop time, goods flow and operation at stations and yards etc are the software issues. It is a matter of operations research. In order to analyze the benefits of MAS, computer simulation must be used.

Computers in Railways 277

There are many methods to conduct computer simulation. For MAS, the simulation can be carried out at least at the three levels.

The first level is the control simulation of train operation in blocks. The task of the simulation is how to obtain the minimum interval of train operation in block. The basic models for the simulation are the expressions (6)—(13). By the simulation, the influence of the different following trains methods (passenger train to passenger train, passenger train to freight train, freight train to passenger train, freight train to freight train) on carrying capacity in the block is discovered, which can be used as the basic data and fundamental method for dispatching operations.

The second level is the control simulation of train operation at stations.

The task of the simulation is to calculate the different transport efficiency of MAS on the conditions of the different station structure, the different transport organization and operation at stations.

The control simulation of the dispatching operation is the third level at which there are a lot of the simulation contents. It includes static simulation and dynamic simulation. The static simulation means that the optimal train operation graph is obtained in a dispatching section. While the dynamic simulation is how to restore quickly the normal train operation when the existing train graph is disturbed. It is required that the optimal result should be found by the simulation. For both of the static simulation and the dynamic simulation, the simulation at the dispatching level must be conducted based on the certain indexes, such as wagon hour, locomotive hour, the turnover of rolling stock, the satisfactory degree of passengers (the shortest travel time), the minimum energy consumption and the shortest crew working time etc.

In addition to the simulation of transport organization and carrying capacity, there are also the other simulations for MAS in terms of its own structure, such as the hardware structure simulation, the software structure simulation, the transmission simulation of communication and information control etc. The objectives of these simulations are mainly for reliability, availability of the system and reducing the cost.

Moreover, the macro-simulation at the higher level can be conducted further to obtain the more benefits of MAS. It should include the carrying capacity simulation at marshalling yards. It is obvious that the reasonable layout of marshalling yards and the design of receiving-dispatching capacity at station relate directly to the benefits of MAS.

The simulation for the connection of railway computer network and MAS is another important topic to directly give play to the benefits of MAS

278 Computers in Railways

One of the advantages of the national railway computer network is to get quickly information concerning train operation and process it. It can provide an optimal dispatching scheme for train operation management. MAS can automatically generate the information in real-time way. The aim of the simulation is to find how to connect the two systems so that the best scheme for train operation management can be obtained.

6 Conclusion

With rapid development of electronic, computer and telecommunication techniques, MAS will be developed further and become the trend of railway control and management. During the development of MAS, in addition to finding a solution to reliability of the hardware and software structure of MAS, adaptability and reducing its cost, the questions must be asked what the benefits MAS can bring about on earth, how the benefits are calculated, compared with FAS, what advantages MAS have in terms of its cost performance. In the paper, the advantages of MAS are analyzed in the aspect of transport efficiency. The initial analysis has shown that MAS can increase carrying capacity in block at least by 20% — 30%, compared with FAS. Moreover, on the condition of MAS, elastic dispatching and optimal control management can be implemented by train operation organizer and a better environment is provided to explore the transport potential. Of course, carrying capacity enhancement does not only depend on carrying capacity in blocks, but also on carrying capacity at stations including marshalling yards. It is considered that the overall carrying capacity enhancement can be implemented in the two steps. The capacity in blocks is the first step. At least, it solved partially the problem.

The computer simulation is an important part of the development to MAS. It can prove the carrying capacity increase after the application of MAS and find the optimal dispatching scheme to implement elastic commanding to train operation. It needs to be developed further.

References

1. Wang Xishi, Automatic Regulation Of Railway Traffic in Blocks, Part one: Railway Signaling and Its Remote Control, pp 1 - 16, Research Report, Beijing Railway Institute, Beijing, 1963,3

2. Wang Xishi, Ding Zhengting, Wu Yunxi, Lu Youxun, Telecontrol

System for Moving Objects —- Telecontrol Equipment in Radio Autoblock System of Railway Traffic, pp 1 - 1 8, Research Report, Beijing Railway Institute, Beijing, 1963,7.

3. The Railway Ministry Standard of the People's Republic of China, Train

Computers in Railways 279

Traction Calculation Regulation TB1407 - 32, Beijing, 1983,1

4. Wang Qihuang, Train weight, speed and density, Chinese Railway Print

House, Beijing, 1990

5. Hu Siji, Theory of train operation organization and carrying capacity, Chinese Railway Print House, Beijing, 1993

6. Yang Zhaoxia, Ji Jialun, The feasibility analysis of development and research on moving block system — Tram Operation Organization, pp 1 - 21, Research Report, Northern Jiaotong University, Beijing, 1993