Defining of factors for the improvement of suburban traffic in Zagreb metropolitan area.

Haramina, Hrvoje ; Brabec, Dean ; Slavulj, Marko 等

1. INTRODUCTION

Defining of improvement factors of suburban traffic represents a significant enhancement of its future development in the Zagreb metropolitan area. The results of past research (Brkic et al., 2001) include models that understand substantial investments in the construction of new infrastructure which would result in the increase of the transport capacity and the quality of providing transport services in suburban traffic, requiring at the same time substantial financial investments. Besides, it may be assumed that such an improvement of this traffic system can cause the occurrence of major increase in the demand for the transport service in the suburban traffic which would in that case, without additional system improvement measures, result in its overload, including also reduced quality of the transport service.

The development of dwell time calculation model of (Buchmueller et al., 2006) represents an example of searching for an optimal solution regarding the utilization of the existing transport capacity of the railway lines intended for suburban traffic, but not its increase. It is, namely, very difficult to define in advance the optimal mentioned stays of trains without a systemic approach to the improvement of the rail traffic control system in a certain control area as a whole.

Suburban rail traffic in the metropolitan area of the City of Zagreb operates on four relations that originate at the Zagreb Main Railway Station as the centre, and propagate in the direction towards the East, West, Southeast and Southwest. The first relation is Zagreb--Dugo Selo in the length of 20.8 km which accommodates 7 stops. The second relation is Zagreb Harmica in the length of 26.8 km which includes 13 stops. The third relation is the Zagreb Main Railway Station--Domagovici in the length of 35.7 km which accommodates 9 stops. The fourth relation is the Zagreb Main Railway Station--Turopolje in the length of 24 km which includes 6 stops. The traffic operates in the period from 4.30 a.m. to 1 a.m. The rolling stock consists of electromotor units intended exclusively for suburban traffic as well as regional and long distance conventional trains that on their way through the metropolitan area of the city of Zagreb perform the function of suburban trains. These trains are not fully adapted to suburban traffic regarding fast exchange of passengers and their throughput capacity within the vehicle, and this significantly affects the stay of trains at stops which results in longer travel times. According to the 2007/2008 timetable the total number of suburban trains amounted to 341 with about 141,514 passenger places per day. According to the data on the number of issued tickets it was found that over the recent several years the number of carried passengers has been constantly increasing.

Traffic control is implemented locally in such a way that signalmen at railway stations regulate the train operation, and the control is performed by train dispatchers who coordinate traffic in case of events that had not been planned by the timetable. The railway line is intended for combined traffic, which means that apart from the suburban trains it is also operated by other types of trains for the transport of passengers and a number of cargo trains. Consequently, it is important to emphasise that the traffic of suburban trains is also affected by the disturbances in the timetable in the wider area of control. The train control system is based on the operation of electro-relay signal-safety instruments for the security of the open rail line and the railway station areas. Train headway on open railway lines operates in a spatial gap of the length of two fixed block sections, and the minimal headway is determined according to UIC recommendations.

2. CENTRALIZATION OF TRAIN CONTROL AND INCREASE IN THE RAILWAY LINE THROUGHPUT CAPACITY

The local method of rail traffic control as has been implemented until now on the railway lines for suburban traffic of Zagreb is limited regarding traffic control coordination for several reasons. The first is certainly the obsolete train control system based on the classical classification of railway lines into fixed blocks with the length adapted to trains whose speed is higher than the speed of suburban trains with longer defined braking distance than the one of suburban trains. This means that the length of fixed blocks has not been well adapted to the operation of suburban traffic, and this results in the reduced track capacity. Besides, in order to avoid bottlenecks in the network, and this refers primarily to the Zagreb Main Railway Station which is the main node in the railway lines network intended for the suburban traffic, it is important to increase the possibility of acting on the train regarding the control of suburban trains by introducing the cab signalling system and the automatic train operation system (ATO). This requires sophisticated (not expensive) equipment on-board the trains as well as in the control centre, which would enable energy efficient driving as well. Given the very high precision of the automatic controllers, even challenging strategies like synchronisation of accelerating and braking trains can be put into practise (Hansen & Pachl, 2008). Another reason is insufficient communication among the personnel who participate in the traffic control and train control process. In this case, namely, the optimal solution lies in the centralization of the rail traffic control in the area of suburban trains operation. It encompasses the introduction of the central train control system (CTC) with the application of automatic route setting and the dispatchers as decision makers regarding the traffic control method in the area of central control. This form of control means also the application of the decision support system (DSS) for the dispatcher in the process of central railway traffic control which helps the dispatcher in identifying conflicts between the trains in the process of timetable realization within a shorter future period of time and provides proposals for their solution. Since the fitting of the mentioned system requires substantial investments into the adaptation of the rolling stock intended for suburban traffic and that, anyway, this rolling stock is already obsolete, the best solution is its replacement by vehicles whose design characteristics would be more adapted to the transport of passengers in suburban traffic and thus it would be possible to achieve significant effects in the increase of the railway line capacity. By reducing the time of stay at stops, namely, because of the higher speed of passengers getting on and off the train, it is possible to reduce the train headways.

3. INTRODUCTION AND MEASURES TO INCREASE THE RELIABILITY OF CLOCK FACE TIMETABLE

Regarding the data on the traffic quality obtained by the analysis of timetable realization in the period over several recent years and the fact regarding the increased demand for this transport service it is important to undertake measures to increase the reliability of the future timetables which plan an increase in the number of suburban trains. It is also necessary to introduce the clock face timetable in order to reduce the travel time that includes transport on several relations. Introduction of the clock face timetable with the increase in the number of suburban trains results in the possibility of the formation of bottlenecks in the network, first of all in the area around the Zagreb Main Railway Station which represents the central node of the railway line network for the suburban traffic. In order to increase the capacity on those network sections where there may come to the bottleneck effect, a train control strategy should be defined with the emphasis on the continuous influence on the trains and the application of ATO. In this way the train operation could be controlled with greater precision and thus the collision between trains would be avoided in case of smaller delays in case of having a timetable with small time tolerances regarding the train headways, their timetables and stays at the stops.

4. MEASURES FOR SAVING OF ENERGY CONSUPTION OF SUBURBAN TRAINS

The saving measures regarding the suburban trains energy consumption are reflected in the manner in which the train timetable is made in the area where suburban traffic operates, and in the continuous method of influence on the train within the train control system. These measures include the timetable in which the travel times are additionally prolonged for a certain amount which allows train operation at lower speeds than the usual ones, thus contributing to a significant saving of the propulsion energy.

Since there is continuous influence on the train, in case of need, it can at any moment increase the speed and reduce its travel time until a certain place on the railway line. This place may be a stop at which a certain number of passengers wait and whose embarkation time assumes a period of time that is longer than the planned timetable. In that case the time saved by reducing the timetable of the respective train may be used to prolong its stay at the stop thus avoiding train delays in leaving the stop, and in case of normal traffic flow which understands train operation at a lower speed significant saving of energy would be achieved. Additional energy could be saved through the implementation of driver interfaces that could communicate more precise driving instructions to train drivers in real time. Providing train drivers with more precise train operations information should lead to additional energy savings (and/or improved customer service) (Schobel et al., 2009).Recently, dynamic related driver advisory systems have been developed, which permit driver support under all operating conditions.

5. CONCLUSION

The development of the operative management system stimulated by the application of computer technologies provides the possibility of improving the railway suburban traffic regarding its optimization and meeting of the increasing demand for this transport service. The mentioned factors represent a precondition for systemic improvement of the rail suburban traffic in the Zagreb metropolitan area without major investments in the rail infrastructure. This would increase the throughput and transport capacity of the railway lines as well as result in a significant increase in the quality of the transport service which is reflected in reducing the train delays and the speed and comfort of travelling.

The future research should be carried out regarding the connections between the rail traffic control system and other traffic modes that also participate in the provision of transport services to the passengers within the metropolitan area of the City of Zagreb, that would provide greater flexibility of timetables. The structure of such a traffic system would be defined based on the comparative advantages, and also the redundancy which would allow monitoring of the passengers' satisfaction with individual types of the transport service on certain relations which would help in defining the future parameters of the respective system.

6. REFERENCES

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Hansen, I. A. & Pachl, J. (2008). Railway Timetable & Traffic, Eurailpress, ISBN 978-3-7771-0371-6, Hamburg

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