IMPROVING THE POSITIONING ACCURACY OF TRAIN ON THE APPROACH SECTION TO THE RAILWAY CROSSING

Dep. «Automation, Telemechanics and Communications», Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St., 2, Dnipropetrovsk, Ukraine, 49010, tel. +38 (056) 373 15 04, e-mail diitats@mail.ru, ORCID 0000-0001-9954-4478 Dep. «Transportation Technology», Lviv branch of the Dnipropetrovsk National University of Railway Transport named after Academician V. Lazarian, I. Blazhkevich St., 12a, Lviv, Ukraine, 79052, tel. 38 (032) 267 99 74, e-mail ovozom@gmail.com, ORCID 0000-0002-7163-9026 Head Dep. «Automation, Telemechanics and Communications», Ukrzaliznytsia, Tverska St., 5, Kyiv, Ukraine, 03680, e-mail soyuz_at@mail.ru, ORCID 0000-0001-6833-964X


Introduction
Railway crossings as crossing places in the same level of the railway roadbed and highway are one of the most dangerous areas for the rail and vehicular traffic.Safety control at railway crossings is one of the most acute questions of the general problem for traffic safety on the railways.In accordance with the conducted analysis, the number of road traffic accidents at railway crossings in recent years has decreased significantly in Ukraine, but is still quite large and is accompanied by significant material and human losses (Fig. 1).Analysis of accidents at railway crossings in different categories (Fig. 2) showed that their considerable quantity (more than 60%) occurred at crossings equipped with automatic crossing signaling (ACS) without a crossing tender.A similar situation is typical for other countries.For example, in Europe more than 300 deaths occur per year due to accidents at railway crossings [10], and most of them happen at open railway crossings.The main cause of road traffic accidents at railway crossings is noncompliance with rules by drivers of vehicles, namely, transit through the crossing after the pre-alarm application before the approaching train.
For the timely detection of obstacles before the approaching train at railway crossings many methods were proposed, including ultrasonic detectors usage [11], radars [9], satellite positioning [16] and other sensor devices [8.17], as well as using video surveillance the rail crossing zone [12,13,15] with information transfer to the train driver.
Vehicles entry at the railway crossing after the pre-alarm application in some cases is provoked with unreasonably high latency time of train's passage, which can be 12 minutes or more.This is due to the fact that the actual motion speed of different trains can vary greatly, while ACS switching occurs at the train entry to the approaching area with the fixed length, which is calculated on the maximum speed of the train.
Thus, in order to improve movement safety at railway crossings it is necessary to use additional means of control, allowing to inspect the zone vacancy of railway crossing, as well as the section of approaching the train to the crossing with automatic determination of train position and speed.
A great number of methods and devices of automatic crossing signaling based on the actual speed of the trains and coordinates at the approaching section, that are determined by the signals from the point sensors of different design, placed on the approaching section to the crossing are described in the literature.However, none of these devices was not widely used due to the lack of functional safety.It is worth mentioning the measuring methods of train coordinates on the approach section to the crossing, based on changes of parameters control of the rail line during the train movement on it.The [2] proposed a method based on test signaling supply in to the rail line, [6,14] proposed to measure the distance up to cuts on the marshaling yard, based on signal processing of track circuits using the states classifier.The authors [4,5] proposed to determine the train coordinates by input resistance of the track circuit (TC), on which there is a train.Since the accuracy of these methods is significantly affected by the ballast insulation resistance of rail lines, the authors [4][5][6]14] offered to analyze the measured signals and parameters of track circuits using different state classifiers of track circuits.However, complete research for the changes impact of ballast insulation resistance on the on train positioning accuracy has not been studied sufficiently.

Purpose
Purpose of this paper is improving the positioning accuracy of trains on the approach section to the railway crossing that eventually will increase traffic safety at them.

Methodology
Research were conducted with the mathematical model method on the developed model that describes the input impedance dependence of the coded and audio-frequency track circuits on the train coordinate at different values of the ballast insulation resistance for all signal current frequencies that are presently used in track circuits.
Mathematical model.Equivalent circuits of the coded track circuit with signal circuit frequency of 25 and 50 Hz and jointless audio-frequency track circuit with frequencies of 25, 50, 420, 480, 580, 720, 780 Hz in the presence of a train on it (i.e. in shunt mode operation) are presented in Fig. 3. , U I -input voltage and current at the output, supplying TC (transformer, frequency convertor or track filter for AFTC); , a a U I − voltage and coded current of automatic signalling for audio frequency track circuits; a C -capacitor in the current supply circuit of cab signaling; CL -four-pole network, corresponding to the cable line for audio frequency track circuits; B -four-pole network, including all equipment of TC supply end, located in the track box or the relay case near a rail line (transformer, impedance-bond resistors, capacitors in accordance with electric circuit of TC [3]); a Z -the input impedance of the adjacent track circuit (for jointless track circuits); ( ) RL x -four-pole network, corresponding to the rail line with the movable unit (train) at a distance x from the supply end; S Z - impedance of train shunt; r Z -impedance of the rail line after the movable unit.Parameters of RC elements and coefficients of for-pole network for matrix in A -form are taken from [3].The primary parameters of the cable and the rail lines at the frequency of the current signal were converted into the coefficients of four-pole network similarly (as in) [1,3,7].The general matrix accordingly to the equivalent circuits (Fig. 1) was calculated as the matrix product of all four-pole network, included in it The input impedance of the track circuit with the movable shunt on it is found by formula: (2, 2) The above mentioned mathematical description is implemented in MatLab.The selected variable parameters included the following: signal current frequency f equal to 25, 50, 420, 480, 580, 720 or 780 Hz; length of the rail line L and the current coordinate of the movable unit 0..
, and the ballast insulation resistance i r .

Findings
The simulation resulted in obtained dependences of the input impedance of track cicuit in shunt mode

( )
, , i Zinp x f r on TC parameters.Simulation was performed for the coded track circuits with signal current frequency of 25 Hz, length of 2.5 km and 50 Hz, length of 2.6 km at two values of ballast insulation resistance i r , equal 1 and 50 Ohm/km.For audio-frequency track circuits simulation was performed for signal current frequency of 25, 50, 420, 480, 580, 720 and 780 Hz at a RC length of 0.  The figure shows that absolute error in determining the coordinate deltax increases significantly with raise 0,5 km x > and at maximum value x L = the relative error is ~40-50 %.
Thus, it can be concluded that the direct use of the method for determining the train coordinate accordingly the input impedance of the coded track circuits does not provide the necessary accuracy for practical use due to the significant impact change of ballast insulation resistance.To reduce error of the coordinate measurement in [4,5] proposed the use of the additional measurement results processing using the classifier of track circuits states.
For the coordinate 0,5 x km ≤ error of measurements x accordingly input impedance is not significant one.
Based on research the paper proposed the method of accuracy increase of determining the train coordinate on approach section to the railway crossing, equipped with audio-frequency track circuits.It comprises the simultaneous usage of discrete and continuous monitoring of the train's position.Discrete monitoring is carried out by signals from track relays of audio frequency track circuits in accordance with the control scheme concerning sequence of occupancy and clearing the track circuits.Continuous monitoring is based on the input resistance dependence of audio frequency track circuits on the train coordinate.
This method is implemented due to widespread introduction of automatic block signalling with audio frequency track circuits instead of the numeric coded automatic block signalling, occurring in recent times, supports implementation of this method.According to typical materials for the crossing signaling design for sections, equipped with automatic block signaling with audio frequency track circuits, for crossing signaling operation for each track near crossing, two track circuits, usually with a common feed end and with a frequency of 720 Hz for one track and 780 Hz for a different one, length of at least 150 are provided.The rest of approach section to the railway crossing in the right and the wrong directions includes several audio frequency track circuits.Prior to approaching section audio-frequency track circuit also has a short length and frequency of 720 or 780 Hz, which allow reducing the area of the additional shunting, and, respectively, to record more Calculated dependence r Z on x is presented in Figure 9. From the above dependence one can be seen that relative values of change ( ) Measurement error of train coordinate upon the input resistance of track circuits on tonal frequencies is significant and these results application to determine the position of the train is only possible after the appropriate intellectual processing of measurement results.
Since the input impedance of track circuits is a complex quantity, the behavior of each of its components is of interest, depending on the train coordinate, frequency and the ballast insulation resistance to select the most suitable complex impedance component for the practical use.Im Z from frequency and train coordinate.From the analysis of the mentioned graphs one can conclude that the most appropriate value for determining the coordinates x is considered above ( ) r Abs Z modulus, since the rest components dependences of complex value of the input impedance of track circuits on coordinates x has more complex nature, which may lead to ambiguity of measurement results interpretation.The results obtained at simulation for other lengths of track circuits and of cable line have shown that the above considered regularities are performed for them too.

Originality and practical value
The developed mathematical model allowed determination of the error dependence of the train coordinate upon the input impedance of the track circuit for coded and audio-frequency track circuits at various frequencies of the signal current and ballast insulation resistance.
The paper proposed the method for train location determination on approach section to the crossing, equipped with audio-frequency track circuits, which is a combination of discrete and continuous monitoring of the train location.Discrete monitoring is carried out by signals from track relays of audio-frequency track circuits in accordance with the control scheme concerning sequence of occupancy and clearing the track circuits.Continuous monitoring of train position is controlled with the input resistance of audiofrequency track circuits.

Conclusions
1.A mathematical model was developed; it describes the dependence of the input impedance of coded and audio-frequency track circuits on the train coordinate at different values of the ballast insulation resistance for all usable frequencies of current signal in track circuits.
2. Relative error of detecting the coordinates of the train by input impedance of the coded track circuits due to the change of ballast insulation resistance was determined.It can reach 40-50%, which makes impossible a straight-forward adaptation of a method for determining the coordinates of the train by the input impedance of the coded track circuits.
3. For the audio-frequency track circuits at frequencies of automatic cab signaling the relative error in determining the coordinate of the train by the input impedance does not exceed the acceptable values, it allows using this method to determine the train location on approach section to the railway crossing.

Fig. 1 .
Fig. 1.The total number of road traffic accidents at Ukrainian railway crossings (1) and the number of victims (2) during 2007-2013 years

Fig. 2 .
Fig. 2. Distribution of road traffic accidents by types of railway crossings: 1 − unmanned, equipped with ACS; 2 − unmanned, without ACS; 3 -with man on duty and signalling; 4 -with man on duty and without signslling; 5 − outside of a railway crossing

Fig. 3 .
Fig. 3. Equivalent circuits of the coded (a) and audio-frequency (b) track circuits in a shunt mode In the figure, there are following designations: -1 1 , U I -input voltage and current at the output, supplying TC (transformer, frequency convertor or track filter for AFTC); , 3 km and ballast insulation resistance i r 0.8 and 50 Ohm / km.Cable line length is taken equal to 1 km.The simulation obtained dependences of the inis not significant, but when x is in- creased this impact becomes essential that does not allow determining the train coordinate x by input Наука та прогрес транспорту.Вісник Дніпропетровського національного університету залізничного транспорту, 2016, № 1 (61) АВТОМАТИЗОВАНІ СИСТЕМИ УПРАВЛІННЯ НА ТРАНСПОРТІ doi 10.15802/stp2016/60936 © V. I. Havryliuk, O. M. Voznyak, V. V. Meleshko, 2016 impedance of track circuits ( ) , , i Zinp x f r with sufficient accuracy for practical usage.

Fig. 4 .
Fig. 4. Dependences of the input impedance modulus of the coded track circuits on the coordinate x To study the impact of ballast insulation resistance changes i r on the train coordinate accuracy x accordingly value Наука та прогрес транспорту.Вісник Дніпропетровського національного університету залізничного транспорту, 2016, № 1 (61) АВТОМАТИЗОВАНІ СИСТЕМИ УПРАВЛІННЯ НА ТРАНСПОРТІ doi 10.15802/stp2016/60936 © V. I. Havryliuk, O. M. Voznyak, V. V. Meleshko, 2016 precisely the entry of the train on the approach section.Fig. 6 presents the dependences of input impedance modulus ( ) abs Zinp audio frequency track circuits (TC) on coordinate x train for signal current with frequencies of 420, 480, 580, 720, 780 Hz and for ACS current, frequency of 25 и 50 Hz at 0,8 Ohm/km i r = are presented in Fig. 6.

Fig. 6 .
Fig. 6.Dependencies of input impedance modulus ( ) abs Zinp of audio-frequency track circuits on x for different frequencies As it can be seen from the figure monotone dependence ( ) abs Zinp on x allow using it to determine the train coordinates at all tested frequencies.The resolution capability of the method depends on change rate of the input impedance of track circuit Zinp by variation x .To evaluate rate of change Zinp from x at different frequencies the derivative from Zinp upon x was calculated ( ) [ ] ( ) ( ) abs Zinp dif abs Zinp x ∂ = ∂ .Fig. 7 presents the dependence of derivative ( ) ( ) dif abs Zinp on x .One can see that graph

Fig. 8
Fig. 8 presents the dependence dif Z on the coordinate x for frequencies f =25, 50 420, 480, 580, 720, 780 Hz is presented in Fig. 8. From this Figure one can see, that value ( ) dif Abs Z is significantly increased by raising the coordinate x and signal current frequency.It should be noted, that obtained values are large enough ( ) dif Abs Z and they do not fully characterize the error of measurement.To characterize the relative measurement error, let us consider the relative change of the TC input impedance ( ) , inp i Z x r , caused by changes of the ballast insulation resistance ( ) Fig. 10 presents the graphs of complex impedance compo-nents of the track circuit, namely,