The Railway Operational System Architecture (ROSA) has been designed taking into account combined findings from the literature review and on-site observations. As shown in Section 2.3.1, railway operations rely on the coordinated function of operators with the rolling stock and infrastructure. Therefore, the ROSA comprises four main components: (i) the train, and in particular the train cabin, (ii) the control centre, (iii) the signalling and controlling systems and finally (iv) the communication systems. The basic concept of the ROSA represents the interconnections between the two main operators, i.e. train drivers and signallers2, in conjunction with the on-board train systems, the signalling and control and the
railway communication systems. The ROSA is presented in Figure 2-12.
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Figure 2-12 The Railway Operational System Architecture (adapted from Rail Safety and Standards Board, 2009 and modified)
As shown in Figure 2-12, the ROSA railway communication means include the legacy conventional radio and modern telecommunication systems (Smith et al., 2013). For the UK main line network, for example, the Cab Secure Radio (CSR) and National Railway Network (NRN) are the main radio systems. On the other hand, the Global System for Mobile Communications-Railways (GSM-R) represents the modern telecommunication system, mandated as standard for the European railways by the European Commission in 1997. With respect to the signaling and controlling of train movements, a number of protection systems are being implemented. Again, in the case of the UK network, apart from the signals (open, at station, at yards), which inform train drivers whether they should proceed, slow down or stop the service, on board and on track safety systems are installed. These include those identified in Section 2.2.2.1.2 (AWS, TPWS and ATP) with additional countermeasures implemented to assure safe train movement. Such measures include axle counters, which are track mounted equipment to count the number of axles on a train along the route and the track circuit (see Section 2.2.2.1.2). Further to the received amount of information from the signaling and controlling systems, an additional set of data flows between the components of the ROSA, informing the operators of the current and overall operational profile. The set of data is classified by the RSSB (2009) as:
• Near real time data, which are delivered within less than 30 seconds (excluding the Piccadilly Line operations).
• Quasi-static data, which are either given at the start of the journey or on a daily basis. • Static data, which are given when infrastructure, rolling stock or any other changes
are made.
Under the assumption of normal operations, train drivers, before starting the operation, are updated by receiving the quasi-static data essential for planning an appropriate driving strategy. The signallers and controllers, on the other hand, who have set the routing of trains on the entire network, inspect and confirm that the services are operated as scheduled. During the journeys or train movements, train drivers constantly receive near real time data and information by the signaling and controlling systems. In addition, signallers and controllers, receive information on their panels with respect to the location of each train along the network. All the exchanged information is indicated in Figure 2-12 by the black arrows. It is shown, for example, that a train driver receives information from the signals while the panel is being updated based on the location of the train relative to the locations of the other trains on the network. Further, signallers and controllers receive also information from the signaling and controlling systems. They use this information to maintain the traffic on the network or perform any necessary changes, aiming at resolving any potential conflict between the trains.
It is apparent from the ROSA that the safety of railway operations depends on the reliability and quality of the technical systems, as well as on the performance of the relevant operators. Again, assuming normal operations where no technical failures are reported, it is sound to claim that either the actions or inactions of operators or any external to the operational scheme factors, e.g. trespassers, can compromise the safety of operations. For example, a train driver who does not acknowledge the received information may maintain the train’s speed above the permitted limits, leading to a signal passed at a danger (SPAD) (Dhillon, 2007). However, even under the assumption of technical failures, the performance of operators remains significant with respect to the safe operation of the system. For example, in the case of a failure of the signalling system or on a train, depending on the size of the disruption, new routings may be required, which could be complicated to set and therefore, any wrong actions from the side of signallers or controllers may jeopardise the safety of the system (Dhillon, 2007). Therefore, railway organisations should define and further examine the causes and factors that have an impact on the performance of railway operators, in order to enhance performance of their employees.
2.4
Summary
This chapter started by a review of the evolution of railways over the years. This was followed by the description of the modern railway system and a detailed analysis of its main components, elements and stakeholders. Based on this description, this chapter then introduced the operational concept of the railway system, from the perspective of operators, referred to as the Railway Operational System Architecture (ROSA). The ROSA displays the operational constituents, and identifies the interactions between operators, equipment and transmitted information. In addition, ROSA has facilitated the identification of a number of issues that should be taken into account concerning the safety of railways operations, including the reliability of infrastructure and rolling stock as well as the significant influence of human performance. The next chapter investigates the contribution of each component of the railway system to the overall safety of railways.